I changed from a 16 to a 17. The difference was about 5 mph- the rpms at 70 on the 16 were the same as 75 on the 17. Definitely noticed a difference on the low end pulling out but nothing I didn't get used to after a few rides. The 17 is perfect for me as I don't want to give up any more low end. Someone on the Triumphrat.net site has a rpm calculator spreadsheet that seems to be right on.

2005 Speedmaster, Tornado Red, AI removed, Uni Pods, JCW 19" turnouts