I used the 7.5mm 180cm shaft exclusively on my trip. This was only my second trip with this gun. On the first trip, I remember thinking how accurate the gun was and it seemed that I couldn't miss a shot. On this trip, I missed quite a few shots, which I'm sure has a lot to do with my inexperience. It might also have been a matter of just getting used to shooting with the longer shaft. For this trip I also replaced the double 14s with double 16s, and so it wasn't only the shaft length that changed.
One thing I did notice was that the gun seemed to be nose-heavy with the extra 10cm overhang. I guess I'll have to use the gun again with the 170cm shaft to confirm all of this.