Thanks for more rom suggestions!
Also, thanks to all those who suggested roms to use, I've read the thread every time it's been updated.
Just for everyone's info, I ended up installing CM7 ILWT - it's been excellent. Fast, stable, things work - it ticks all the boxes, really, and it means I can squeeze a few more months out of my phone! Actually, it's made me rethink upgrading next year.
It's been fine for my needs and I'm no longer pulling out my hair in frustration; there's no lag, no issues with functionality, and everything is in English (rather than Chinese, like MIUI's calendar lol - also the stock player doesn't make all my album covers turn to "Jamon - The Power Of Love" too!)
I may do a nandroid backup and try some of the other suggestions. I am a little bit reluctant to try any ICS roms, I've read posts describing things as being smooth but lots of things not working properly... I may give them a try anyway and see, but I am wary. One persons buttery smooth is another persons laggingly slow. I'd prefer to do away with flashy stuff for a phone that.. um.. "just works", and fast.