I went from a Fazer 600 to the V-Strom 1000, mainly to get more torque and comfort for the pillion. The owner of the local Suzuki dealers had run my 1000 as a demo bike and loved it, then went to the V-Strom 650. He's still riding the 650 6 years later, and recently said "it's all the bike I'll ever need", but that I would miss the ccs two-up. This from a guy who could ride anything from Suzuki for nothing...
I've not ridden the 650, but the ergonomics are the same as the 1000, and it's really comfy for long days riding...
Neither have the same top speed as the Fazer 600, but the grunt from the v-twin is addictive, and unless you want to risk your licence, who needs more than 110mph anyway?