Sorry to jump in here hpd. What's 5cm after all? It also depends on what you like to do. I got them to be able to make shorter turns than my 170 Atomic SX:11's. They still hold great at speed at 165. That being said, with a slightly longer turn radius I'm sure they'd be great at 170 too.
Snomiser, if your husband's style and ski preference aren't too strongly towards short turning, the 170 would be fine - the RX8 is one of the best skis around - it does it all - go for it. Ice, crud, groomers, bumps. And the 03/04 model is beautiful and the same ski as the 04/05 except for a slight difference in the binding mounting.