AO Gold Member
Join Date: Jun 2007
Location: United Kingdom
Have a look on XDA in the specific forum for your model. There will almost certainly be a customised version of Cyanogen on there.
Make sure you follow the instructions for unlocking your bootloader, installing custom recovery and gaining root to the absolute letter and you will be fine.
Yes, any ROM by a recognised developer will improve the responsiveness of your phone and may even add some decent features.
I wouldn't bother with Sense ROMs unless you have an HTC though. It will almost certainly be missing features and won't be completely stable.
Stick to optimised TouchWiz (Samsung's UI) or Cyanogenmod ROMs would be my advice.