Yeah - SSF has more characters and online is more improved. Slight tweaks on some of the characters powers.
Ah ... dang. Just checked my collection. I don't have SF4 anymore. I must have traded it in when I got SSF4. Sorry mate. Was looking forward to having a ruck with you too. Let me know when you get SSF4 instead.
You've missed SSF4 - Arcade Edition mate! Released on PSN already as DLC but in the shops this week I believe.
Afew differences to SSF4 in that there's 4 new characters (including Evil Ryu) and an improved lobby system, replay channel etc etc. Basically it's the version you'd play if you went into a proper Japanese arcade. A few tweaks but makes the game better IMO.