I believe they are very peaky and will be a handfull offroad. I have a Husqvarna TE610 and it just spins the back wheel when its wet, very frustrating. I would go for a smaller bike like the 404 or a DRZ400, thats what I plan to do.
IIRC, the 604 is the Rotax engine, the 644 is the Suzuki DR650 lump.
As Any T says, the Rotaz was a bit of a pig off road, plenty of grunt but a bit too far up the rev range for some people.
Now I have heard of a tidy DRZ for sale in the Chester area. It is the 'E' model, so electric starter.
I could make some enquiries for you.
The 604 and the 640 were both Rotax lumps. The 644 is the Suzuki lump and arrived in 2002.
Whilst the smaller DRZ engined is much lighter and probably more capable off road, don't dismiss the 644 for off roading. Yes, it's heavier but is more than capable off road and handles light laning with ease and comfort. They're also a bargain buy used, particualrly if you can blag one with both sets of wheels.
I've even off roaded mine on the supermoto wheels on light lanes when I couldn't be bothered to change the wheels. Best buy is 2004 on with the digital dash, but if buying before 2003, check the cylinder base gasket has been replaced, easy to check as the later gasket has a tab with a rivet in sticking out of the base.
If you're looking for a bike to do some light laning, I don't think you'd be disappointed.
Had both sets of wheels, did a weekend ride out green laning with CCM factory (which my brother won in a magazine) and what a laugh, fell off several times but just jumped back on. They wheelie well too.
seeing how this has turned into the "show us your CCM" thread
here's my 604e (rotax) when it was just a few weeks old had it for 3 years
can they be off-roaded?
hell yeh! great fun! a bit lardy, a bit long in the wheelbase but the rotax lump more than makes up for it! took four of us to get mine out of a bog..burried upto the top of the engine