Before we render a conclusion, let's have a look at the overall benchmark results:
Because we had no X4 640 at hand, we just reduced the multiplier by 0.5x to get results. As you can see the X4 645 is just 1.7% faster then it's 100MHz slower counterpart.
Luckily for us, the memory prices are down again. For €60,- you can now get a 4GB kit @1333MHz and CL7. CPU prices are quite stable, but AMD did reduced some of them two weeks ago, which also shows. We stick with our MSI 785GM-E65 board, because we think the quality is much better as the new 890GX reincarnation. On the Intel side we choose this time the MSI H55M-ED55 which droppeld from €99 to under €75 and is just about €3 more expensive as the 785GM-E65. The aged HD4850 is now available for under €80 which it makes it a bargain, compared to the HD5770 or HD6850 and will suffice for moderate gaming.
We are not very fond of the 100/133MHz increases of any manufacture on any CPU. It's quite senseless to increase the frequency so little in the 3GHz age, because it does not make much difference, besides the money the companies will cash it for. AMD saucily charges you with €12/$16 for just 100MHz. Of course Intel does the same with it's CPUs and we don't think that's fair to the customers.
The Athlon II X4 645 is available for about €94.50 or around $116,- while the 100MHz slower Athlon II X4 640 costs you only €81,95 or shy of $100,-. It's quite an achievment for AMD to offer four cores at this price-range and even for gamers, this CPUs should suffice. The more powerful Phenom II X4 945 with 3GHz does cost considerable more with about €119,- or $136,-.
If you are a gamer on a budget any Athlon II X4 will do fine, even when games are sadly not optimzied on the AMD platform. A potent graphics-card will always be more crucial for good framerates then a faster CPU. The overclocking potential has not increased with the faster parts but speed is adequate. Everybody who needs more potential will go with the X6 line, everybody else does nothing wrong buying an AMD Athlon X4.