OEM 16s and OEM 17s have the same overall tire diameter.

 

IMO, this car didn't really need a 17" wheel. However, they tuned the new suspension with the wider tires, so I'm not sure what going back to a 16" wheel would do to handling. I'm sure part of it was a marketing thing, since everyone wants big wheels for that "slammed" look. Playing around with tire sizes with this car may be dangerous. The suspension was tuned for X size and I wouldn't stray outside of that.

Rather than changing tire size, going with a lightweight 17" wheel, like an SSR Comp at about 14lb, would improve acceleration over the fairly heavy OEM wheels that are about 17.5-19.5lb each. Whether it is worth the cost, is another question.

 

I had the 16" S2000 wheels on my car for about 2 months. The wheels is a little bit lighter than the stock 17s and my car did pick up a bit quicker. Unfortunately, in the canyons, the 17's wider patch helped with high speed turn-ins and generally made the car more stable. With the 16s, I felt that the car was a lot less stable during a high-speed turn. This is most likely due to the fact that the new suspension on the 04s were just not calibrated for the 16s. So basically, you lose stability in a turn for better accleration.