I had my heart set on an Acura 3.2CL TYPE S. I was a little dissappointed in it. First off, it is only available in an automatic transmission. Once you feel the power though, it just doesn't matter. It's the fastest of the bunch in a straight line. The first thing I noticed was that it is very front heavy. It doesn't have the 50/50 weight dist. of the german cars and it really showed in its handling. It can't keep up in the twisties with the other cars in your list. The other thing that bothered me was lack of traction from the puny 215 series 17" tires they give you, and noticable torque steer under full acceleration. Other than that....great car....nice interior, very comfortable, comes fully loaded and a GREAT Price!
I only drove the IS300 with an automatic. At the time, it was no contest for the 325i. Besides the styling at the time (which is growing on me), I just was not happy with it's performance and really wanted a manual transmission.
The IS300 with a 5 speed should be compared to a 325i 5 speed. They are both about neck and neck performance wise. the IS300 might be a bit faster in the straight line, but the bimmer has the edge on handling and poise with that beloved sports package suspension. You can't go wrong with either.
If you really want to be ahead of the game and can afford 37-40K, go with a 330i.....that 3.0L engine is amazing.
Another alternative you should consider is the AUDI A4. The new styling is sharp, and it drives very nicely.
Good luck and give us reports after you test drive!