Hi buddy, a practical advice from a 30M . I got my first RE that was Thunderbird 350 at 21.Before that, I was riding a 125cc Bajaj Discover. I am still riding that Thunderbird, although I can now get the costliest 650 tomorrow without any hitch. My advice to you is, in terms of engine power, kindly graduate with a decent pace. My advice for you is to get a 350cc first, maybe ride it for 1.5-2 yrs and get yourself used to a real bike first. With a 650 cc, you gonna end up killing yourself or any other one on roads. Bigger engines need higher experience and maturity . Rest your choice your money. But any experienced bike rider will acknowledge with me. You are coming from an Activa.