Hblair,
matey think about this one. If you want to work out then a long ride in the country on a 4 stroke is gonna be your thing, heavy mutha of a mike with bags and bags of low down grunt. See, it's not hangin on to the bike that gives you the work out, it's forcing the bike to do things it doesnt really want to do (like run over logs), the heavier the bike the more you've gotta work.....and you can do this kinda stuff at lower speeds.
If you want a adrenalin surge and a real quick work out while the hill disappears under ya then go for a 2 stroke....but be prepared to scream the nuts outta it every where you go (cos thats just the way ya have to ride em) and rebuild the engine every other sunday. However, your work out will be more from hangin onto the thing while you scream the engine, more dynamic tension......you'll feel shrecked afterwards but mainly from acid buildup in your shoulders than a good workout.
And as DjV says, screamin around the place like a maniac = good chance of a big crash and no more AH for 6 months while the docs rebuild bits of ya.
