If you're able to better utilize the GPU, it may help with your speed. Again, given your hardware, you may not notice a significant difference.
Your "best bet" at a playable experience would be to use whichever revision is fastest for you. Just be aware that 3.5 is no longer supported on these forums, so any glitches and bugs you encounter you'll have deal with on your own. 3.5 also had several notorious bugs in a wide range of games. That said, no one's forcing you to upgrade, but be aware of the caveats and "gotchas" when using 3.5.
Your "best bet" at a playable experience would be to use whichever revision is fastest for you. Just be aware that 3.5 is no longer supported on these forums, so any glitches and bugs you encounter you'll have deal with on your own. 3.5 also had several notorious bugs in a wide range of games. That said, no one's forcing you to upgrade, but be aware of the caveats and "gotchas" when using 3.5.