Hi there,
I have the same exact car, and went through the same process. First lets talk about size's
I chose the route of going with 225'/15s all around so that I could maximize tire life by being able to rotate any tire to any position. That works great for me. I use 1/4in spacers on the front to keep them from rubbing on the springs, but the spacers then require longer wheels lugs so you get a good thread on the nuts. (gaaa the slippery slope!)
You can run 16's but not very well in a 225 without serious rolling or trimming of the fender lips to prevent rubbing. Although I FULLY admit that I have never run Tuffy (My 924S) with bone stock suspension or ride height so rubbing may be less of a problem if it were.
The downside of the route I took is that your tire selection gets fairly small. As in just a few possibilities. Fortunatly the Hankook RS-3 is a GREAT tire, dosn't cost much, has decent life, and comes in that size!.

It is a 140TW so you will pay points for it though. I can't speak to the other brands mentioned as I have not used them...however. Just in looking at the sizes. In order to run a 15" you will also have to run a 205 which puts you with a bit less rubber on the road than the 225 and if you want to run the 225 in them you have to use the 16's and face rubbing issues.
I am happy to chat especially about our fine little 924S' pop me a note anytime!
Tuffy getting up on three of those 225's at the Instructor day:
