Rom/radio help htc diamond

[pimped_up]

Hello everyone im very new to the whole windows operating system. I bought an htc diamond CDMA with Bell Mobility. The phone is my fiances and she wants it to be quick and smooth. She wants it to be easy to take pictures, check her messages, and go online.

I have been reading about putting wm 6.5 on the phone (Phone is security unlocked and running Pegasus right now)

I have things about people changing the radio and I have no idea what that is.

I guess my major questions is If I have a stock HTC Diamond what is the best combination do you suggest to make is run quick and reliable.

I have heard about people using roms but other things have been changed also (Cant remember that)