what will you be doing with the computer? from the standpoint of the cpu you have now, you will notice a big difference even going with the Q6600. the Q6600 is cheaper then the Q8200 by a bit but 45nm cpus are 10% faster per clock then 65nm cpus. while the Q8200 has less L2 the only area that has any effect is in programs such as superpi,FAH, low res gaming (ie 1024x768). if you high res gaming or doing av encoding the amound of L2 will not affect performance at all. no only that but the 45nm cpu carries the SSSE4.1 instruction set which in encoding apps that support it, will cut 15mins off encoding times alone. the 45nm cpu will also use less power at stock and oced vs 65nm cpus. now if your using the P5Q-pro as your sig shows, then get the 45nm cpu. you wont have the fsb wall issues that takes place on P35 boards.
if i were just to assume this is only for gaming and on the cheap. i would have to say the Q6600 for those reasons, no need to spend a bit more now on cpu. since in a about 6months time you will more then likly want to move up to the i7 platform.