SEVNT4

I don't think that anyone is doubting that going to a larger size will not be a compromise but it's key to point out how much of a compromise and how you go about minimizing that.

As a side note, I also think that this type of change would be more noticeable in the different model years.

2000-2001 more noticeable
2002-2003 less noticeable than previous
2004-2006 even lesser than previous models

Why do I say this? The ecu is remapped in the 02-03 MY which provides a little bit more power throughout the rpm range. The 04-06 benefits from more power/torque throughout the rpm band as well as a little bit more aggressive gearing in the lower gears making it more tractable during city driving where acceleration is concerned. Some of this stuff is going to make difference between model years IMO but if you compare a car within its own MY, then you'll want to make sure you minimize the impact to the point that worrying about it is negligeable.

While randizzle's point didn't quite come off right, he does make a valid enough point about extracting every last ounce of benefit and the real world useability. We all agree that larger diameter and heavier wheels will make a change but if you stay close enough to spec (and get a light enough wheel/tire), will you really care at the end of the day whether you're a tenth of a second slower to the next stop light? Maybe so, maybe not. Any modification is always a compromise in one direction or another so do your due dilligence if you choose to go 18's and you'll be more happy that way.