Resist the urge to buy an AMD CPU for gaming. You can get an Ivy Bridge i3 for less.
If you're playing at 1080p, 1GB is fine for VRAM. You'll probably want 2GB for newer games with MSAA at higher resolutions, though.
Yes, there is a difference in the RAM speed. I'm not an expert on RAM, but basically the first two sets of RAM you listed are CAS9 and the last is CAS8 (lower CAS is better). The clock speed of the ram also matters (i.e.1333MHz vs. 1600MHz). The two combined affect the response time for the CPU to access memory. That said, even though DDR3 1600 CAS 8 is faster than DDR3 1333 CAS 9, you're probably not going to notice any difference outside of benchmarks. I would shoot for 1600MHz RAM first, then the lowest CAS that looks like a good value. Right now, CPU architecture is inhibiting memory speeds (or in other words, memory won't be a bottleneck for CPUs).