Here is the link to Cathar's post regarding pumps. If you notice it is a bit dated since it doesnt incorporate the newer Laing D5 pump. Cathar's second post down is in regards to running an MCP600/AquaXtreme50z pump at 13.8 volts. If you notice it becomes the second best pump in terms of performance. While 12V is the
nominal voltage for running the pump I believe I have read where they can handle up to 14.2 volts (still digging for the page with the full specs on the pump, will post when/if I find it) so it wont 'burn' the pump quickly. It will however void the warranty
Skip down to Cathar's conclusion at the bottom of his second post in this linked thread for a plain english description for his thoughts on the MCP600 at 13.8 volts. In case you dont recognize the name Cathar has been around WCing for a long long time and has had a huge influence on the performance improvements we have seen across the last few years. While no ones word should be considered the absolute 'truth' when it comes to component performance I would have to say Cathar is one of the more trusted resources for WCing information.
Cathar's Pump Roundup
The current pump favorite is the Laing D5/MCP655 pump but the MCP600 is still one of the best pumps available for performance. It outperformed the D5's older sibling the D4. I think with the release of the D5 the performance gap has been narrowed but the MCP600 still outperforms the new D5. Below $200 if a person is looking primarily at performance it *may* be the best without modding, after modding I think the LaingDDC may surpass it....until you overvolt to 13.8 volts
Keep in mind 'performance' for each person is different. For some its the ability to reach the coolest possible temp while for others its a balance between noise, dependability, and temps. You will have to decide what is most important to you before deciding which pump is 'best'. Short and sweet there is no single 'best' pump in all categories. For raw performance it might just go to one of the $200+ high head Iwaki's while for silence it probably goes to either the Eheim 1048 or the LaingDDC. Most other pumps fall somewhere between these pumps and each has a different 'flavor' which is little more than slightly different balances being struck between raw performance, noise, cost, and dependability.
Lastly on the MCP600. When originally released there were dependability problems with Rev 1.0 but since Rev 2.0 they seem to be pretty danged dependable. Despite this many people have a 'bad taste' from the release version so you will regularly see their dependability questioned.