1. The car says to use 91 octane for best performance. My wife filled mine with regular the first time she took it. I was most displeased, but it ran just fine. My guess is that the computer recognizes the difference with the o2 sensors, knock sensors, etc. and just changes the ignition timing. It loses performance, but keeping you from burning a hole in one of the pistons.
2. I have been very pleased with the handling of my 06 SE-R. It does a great job around town, and in high speed corners. It has a stiffer suspension and better sway bars etc. than the 3.5 SE.
When shopping for cars, I drove a WRX and a few others. I ended up with the SE-R and could not be happier. It is a fun car, and most people do not recognize it as something that's fast... for a sedan.