You do not say what the 600cc sport bike was. So, I really don't know if you are used to the power. A top shelf 600 has more power to weight than the M109. But (big BUT) the weight is what will get you as others have said. I have ridden a few big cruisers and I absolutely hate them. I am a sport bike guy, but I do like cruisers fine. Usually the ones under 1200 cc to 800. They handle weigh less, handle and brake better, a lot more manageable and more maneuverable in traffic.
Oh, another big difference between the sport bike and the big cruisers is the low end torque. It will pull off the line much easier and with more authority at lower revs than the 600 sport bike you had will.
Watch this:
http://www.youtube.com/watch?v=erSrEIuOwX4 it is what happens when somone buys a bike they cannot ride.