How big should my wheels be?

Hey guys,
So there is another MR2 in the family as of today!
My current daily has 235's on the rear on 215's on the front. 
I've had it fast through corners with absolutely no problem.
The new car (My Parents) Have offered to do clean swaps for my current
horrible looking chromies. The only problem is that the width's are 205 all round.
Will this be a massive problem on ranges and if I ever take it to a track?
Cheers guys!

u need to run stagged rims eg 17x8 rear 17x7 front mr2 cam out factory with stagged rims i had the sam size rim all round when i bought my Sw20 and the handleing was crap before i changed back to stagged

I agree with Banner. The stock wheel setup is 14 (in AUS) or 15 (Imports) by 6 and 7 inches, front and rear respectively. Running everything stock with identical tyres all round is oversteer-city. Not much fun unless you like drifting the things.
 
I'm running 17X8 and 17X9 on mine. Different tyres front and rear (Eagle F1's front and Federal 595 SS's rear), but it works quite nicely. I've found that 40-profile tyres give the best response and sidewall flex without being too snappy. Very progressive and predictable. I'd highly recommend going at LEAST 7-inches wide on the front (8 is pushing it. You'll be poking out of the guards and rubbing the coils), but 9 can comfortably fit under the rear.
 
The sizes for my staggered setup is 215/40R17 and 235/40R17.
Getting good grip tyres in those sizes is a total pain unless you cough up big $$$, so I've settled with some average quality street tyres for now, and they do the job.
 
I'll be getting some 18's for track use, but for every day use with some hard driving thrown in, I strongly recommend 17's. They also don't look too big, are legal (provided they don't has too low an offset) and don't stand out to the local constabulary too much.
 
Hope it helps :)