$9700? What town is that? Is the bike new? I've seen an '07 C90 priced at $9700 + tax here in Calgary and that's considered to be a pretty good deal.
I spent a lot of time the other day sitting on both (90 & 109), rocking them back and forth, side to side, and while I know sitting is much different than riding, I did not notice the weight difference. You asked me about my experience - I am a new rider for sure. I took some pretty intensive lessons, put myself through an additional practice regimen and have been riding around town quite regularly for the last couple months. I feel very confident on the 50, and I like the bike, but I'm looking for a little more juice on hills, passing, etc. Also, thinking of doing a short roadie or two this summer and I feel the sheer size of a bigger bike is not only going to give me the performance upgrade, but also more stability on the road. Thanks for your ongoing input.