[Tony M]

Without a doubt, go and try anything vaguely appropriate - even if it's not what you think you want (test rides come free, so make the most of it!).

I currently have a 700, I'm 6'4 in my bare feet, and I think its fine.

I had a 650 a few years ago (2002, I think), but kept it less than a year. As far as I can remember, it used to give me about 48 - 50 to the gallon, maybe a little more, whereas the 700 gives me about 55 without trying, and more if I behave (and that's two-up, most of the time, whereas I rode the 650 on my own). 700 has a bit more go, as well (the 650 was broadly OK, but didn't quite manage the same grin factor), and I reckon the 700 makes a better noise. One of my dislikes of the 650 I had (along with many bikes from the major makers at the time) was that it sounded remarkably bland. The 700 has a little bit of a crackle, and the odd bang and pop on over-run (and yes, I keep the bolts tight!)

If you want to play off-road, maybe the bigger front wheel on the 650 is an advantage - I generally stay on tarmac, so it doesn't really bother me either way.

Both alps are easy to ride, forgiving and handle well - the ABS and combined braking on the 700 doesn't do any harm (good for the confidence, anyway!) - it's amazing how quickly you can bring it to a halt.

In the end, you pays your money . . .

Have fun!