I did this, as it was the only new CWP i could get for my 2wd, and at 100 quid, it was cheap too!

I run 225 45 16 rear tyres which do increase the rolling circumference a little, but I had my speedo redone by speedy cables, so its spot on!

Upsides
It helps if you have a slightly laggy bottom end!
Boost comes in quicker!
The car goes through the gears like a motorbike!

Downsides
Traction is poorer as mentioned
Slightly less top end - but be honest - who uses that?!
Speedo needs recalibrating..

In Summary, one of the best mods I have done to my car! Get involved!

Weeksy