One thing you missed on the PC Specs is your CPU speed and number of cores
Anything beyond 4 cores wont really help.
Your CPU should be a MIN of 2.5 ghz (yes I know some get by with less). 3.0ghz or higher is recommended.
Other stuff:
Make sure your PC is not running in power saving mode (this usually throttles back the CPU speed)
Make sure your graphics driver is set to use 3d acceleration for java.exe (The processfor nvida and ATI are different. do a forum search to find the steps)
Well keep in mind that Minecraft runs REALLY well except for when the extreme lag starts. But before that lag I get 60 fps everywhere (vsync).
Anyway my computers specs are:
- 4xIntel Core i5-2400 @ 3.10GHz
- 7.8 Gig RAM
- nVidia GTX 460 with 1024 Meg ram