I am currently using 225/255 on RE050 Pole Positions and they feel great. Has anyone down sized after going larger and liked it? I don't know if the tires are wear out, but it doesn't feel the same. Plus I don't "feel" like the S2 handles when I had the smaller size but maybe that is just my imagination.

 

You can go with the 245/40R17 on the rear no problem. The 255 on the rear will perform a little better in aggressive driving. The contact patch on the 255/40R17 is closer to the stock size.
If I can help with the tires let me know.