Do the inexpensive mods first, if you haven't already. Opening up the exhaust and airbox, along with rejeting makes a big difference. At that point there is very little difference between the 790 and 865. The big bore change is expensive, especially if you have to pay for labor (I couldn't do it myself) in addition to the parts. Do it only if you planned to do it on a new bike as well. All said and done, there would be very little difference in the two.
I also like the wire wheels and chrome on my bike - one of the reasons I wanted the America over the Speedmaster. What if in a year or two they come out with a bigger cruiser (1200-1500cc)? If I like it better than my TA, I may trade then.
