I have a year old Core 2 Duo 6400 @ 2.13Ghz and 2 GB's of RAM, a Radeon X1300 256MB and a FX 5200 128MB and miraculously it plays all the latest games just fine.
At this point the only thing you will even remotely notice is the increase of cache size on the new processors. Additionally, what is the latency on your RAM, Adam (CL)? That is a big factor in RAM performance. Did Alien Ware tell you what chipset the motherboard uses? Without a stable motherboard, it doesn't matter what processor, ram, etc you put in if you don't have a good motherboard. Also- I know this is a laptop so you don't have a whole lot to go on for hard drives, but maybe think about increasing hard drive cache size to 16MB. If I was going to upgrade anything on my PC at this point, I'd get a new board (instead of the low end motherboards that Dell puts out) and keep my current processor and RAM configuration.