Hi, and welcome.
Check out this thread here it sums up the main differences between the UK and Jap versions.
IMHO, if you want power + performance get an Altezza - but bear in mind it's not gonna have anywhere near the poke of a Subaru Imprexa. However the 4 cyl engine is apparently a lot more tuneable.
If you want more luxuries (leather, heated + electric seats, headlight washers, a radio that actually works in the UK (!), Sat Nav etc.) and a Lexus warranty (very good) then get a IS200. Or even better an IS300!!
Hope this helps.