Well, I'm a pretty good person for the job. Let me give a little history.
The first PPC processors used in Macs were the PPC601 & 601+. The 601 came in flavors from 50-80MHz the 601+ came in speeds of up to 120MHz & some Macs came with a peltier too draw more heat from it. It was on par with the original Pentiums. From there was the 603 & 604 CPUs which were essentially the basis of the latter G3 & G4 CPUs. The 603 had a 8KB L1 cache which caused problems when emulating the software for older 68000 series CPUs. The 603e was introduced soon which doubled the L1 cache & fixed the problems while adding a good bit of performance. The 603e & 603ev shipped from Apple in speeds of 100-300MHz. The 604 was upgraded to a 32KB L1 cache & became the 604e & 604ev. It shipped in speeds of 120-350MHz. The main differences was the inclusions dual FPUs & a more sophisticated architecture which included an SMP unit. It was about 30% faster than the 603e.
The PPC 750 G3 took the basic 603e & tweaked it to run *real* software faster. It also had a larger L1 cache (64KB) & a 512KB or 1MB backside L2 cache that ran at 1/3, 1/2, or full CPU speed that made it a very cool & powerful CPU. Only one 3rd party CPU card was made which used a full speed L2 cache. The 233MHz G3 was as fast as a 350MHz 604e. It was made in speeds from 233-500MHz though the G3 233 & 266 were just marketing ploys. There were no intentionally made G3 233-266s. All G3s slower than 300MHz will run at 300MHz. its maximum FSB was 100MHz (in the past, the PPC processor was never run at its maximum rated FSB of 75MHz so I didn't mention it).
The PPC 7400 & 7410 G4 shares more roots with the 604e than the G3 did. A series that was completely designed by Motorola (that is to say, IBM never touched the G4 except to help manufacture some of them), It includes the double FPU & SMP unit of the 604e but was basically a tweaked G3 CPU with the exception that it included Altivec, or VMX. VMX is a SIMD unit much like MMX, 3D-Now!, & SSE. It is much more powerful than MMX & 3D-Now & performs just as well as SSE & SSE 2. The 7400 G4 came in speeds of up to 500MHz but Apple was stuck at 450MHz for nearly a year because of Motorola's inability to provide the faster chips. If you look back in time, IBM has generally been the producer of the fastest PPC chips. The 7410 was a low power version which can be run as fast as 600MHz. With better cooling some people have hit 700MHz. Because of its short pipeline it will outperform the latter G4 CPUs at the same or similar clock speeds. it shares the same L2 cache design but can use caches as large as 2MB. There is little difference in performance between 1MB & 2MB caches. Its maximum FSB is 133MHz.
The PPC7450 was introduced into the market in 2001. it debuted in speeds of 733MHz. It ended its life at 800MHz with the help of a small die tweak in the form of the PPC7451. It had an improved Altivec unit & L3 Cache support. Its design was flawed in a few areas though. Memory bandwidth was less than the 7400 & 7410. Also its pipeline was a good bit longer (~12 stages v.s. 6 on the earlier G4) then the 7410 & it lost some performance because of it. The L3 Cache which runs at speeds of 200-250MHz adds much performance. Its maximum FSB is 133MHz as well
The PPC750CX & CXe came out shortly before the 7450 came out. It was a die shrunk version of the 750 that included an on chip L2 cache. The CX had a 256KB 1/2 speed L2 cache. the CXe had the same cache but it ran at full speed & ran at speeds up to 600MHz. The pipeline is a short 5 stages & it included a FPU that was on par with the G4. The 750FX increased the cache to 512KB @ full CPU speed. It was planned to go all the way to 1GHz but it could not run at 1GHz at 105°C which has been the maximum rated temperature for all PPC processors since the 603e. The latest G3 is the PPC750GX. It runs at speeds up to 1.1GHz & includes a 1MB fill speed L2 cache. It should be able to reach 1.3GHz with time & with a die shrink to 90nm it could potentially hit 1.5GHz or more. It is amazing what IBM has been able to do with a CPU with such a short pipeline. The CX & CXe have a maximum FSB of 100MHz but the FX & GX can reach a 200MHz FSB according to IBM tech docs. The PPC 750GX never shipped in a retail Mac. It has only been sold in 3rd party CPU upgrades which gives it the distinction of being the only PPC to be used in a Mac without having been included in retail model previously. These lines are all IBM designed & built. The 750GX is expected to include Altivec & clock in at 1.5GHz & higher.
The PPC 7455 & 7457 are essentially the same chip except the 7457 runs cooler (it also can use a 4MB L3 cache but the cache but only 2 is actually used. The other 2 is used as a backup). They build upon the 7450 series & are further tweaked in the area of Altivec & the Integer unit. These processors also supports 48bit memory addressing. They have been clocked all the way to 1.4GHz & some have used water cooling & other cooling methods to hit 1.6GHz. The PPC 7458 is a die shrunk 7457 which uses the 90nm process. It is expected to hit 2GHz & possibly 2.5GHz with luck. It will use a 200MHz FSB where as the 7455 & 7457 have used a 133 or 167MHz FSB. Even with a 167MHz FSB it has a low memory bandwidth which is due, in part, to lackluster memory controller chips.
The PPC970 & 970FX G5 processor is a radically different design. It was designed by IBM & Apple & is based off of the Power4. Using a 1/2 or 1/3 CPU speed Hypertransport FSB, independent data busses to the CPUs. It has a 512KB on chip L2 cache which runs at full speed. It has a better Altivec implementation & has a 32KB + 64KB L1 cache (data, instruction). There is no L3 Cache support which is moot because the high speed FSB makes an L3 cache impractical. The 970 was a 130nm CPU & topped out at 2GHz. The 970FX is a 90nm CPU & tops out at 2.5GHz. It has many of the same problems as the 90nm Athlon & Prescott. Dual Cores are planned. That chip will either be called the PPC975 or 970MP, depending on what rumor site you go to.
The e600 is Motorola's next design. It will include single core & dual core versions & will have an integrated memory controller. It will run at speeds of 2GHz & more. Nothing else s known about it at this point though it hopefully will be more than just another improved 74xx processor with extra features.
The PPC processor is also available in other flavors including the 440 series which I wont go into because they are used in non-desktop applications. I hope this was helpful.
