My answer to that is that 165 is crank and there are greater losses thru the transmission. So it's really more than just 5whp difference. Also...at 19k, the RS isn't nearly as good with:
1) handling
2) looks
3) power (said already)
4) options (stereo, rims, kit, etc.)
By the time I priced out a 2.5, brand new it was 22k, MSRP. The MSP can be had for ~18000 out the door with rebates, etc. Then when he has money left over, he can turn it into a monster because it's already turbo'd. The turbo set-up for a 2.5 rs is ~5000 last I looked. This was my reasoning at the time I bought my MSP, and exactly why the 2.5 rs was knocked off my list.