Being slightly heavier than your average rider (sorry, not callin you fat or anything)...I think a 750 wouldnt be BAD for you.

I know a lot of riders that have been riding for a long time are gonna bash me in this thread for supporting your 750cc decision over a 600. But since you are bigger, and seem to know how to ride alittle already...I say fuck it...get a 750. And if you fuck up on it and wreck, so be it. Live and learn right?

As far as what to look for in a used bike...

For a 2000 year bike, I would not get one with more than 20k miles. Also, the closer to STOCK the bike is when you go to buy it, the better. More than likely (but not always), a hooked up bike means the guy probably rode the bike hard. Thats not to say a stock bike couldnt have been beat up on, but a hooked up bike (I think) is more prone to rough riding.

Other than milage...you probably dont want a bike that has been crashed. A low speed drop probably is not that bad. Like a parking lot drop, or driveway drop is probably okay too.

You want to look at the chain and rear sproket. If the chain is dry or dirty or really loose, it means the rider did not take good care of his chain and more than likey did not take good care of his bike in general. The rear sproket: if it has really really sharp teeth, this is bad...and means you will have to replace it soon. The teeth will be slightly rounded on the tip and not sharp if it is in good condition.

The tires. Tires can be costly. Up to about $300 for a set of new front and rear tires. If the tires are shot, you can expect to put about $300 bucks into the bike immediately. Personally, I do not feel comfortable on a bike with old or bad tires. Good tires can mean the difference between life and death on a bike...especially if your doing 150+ or draggin a knee at 90+.

When you test drive it...
Be very attentive to 2nd gear. A lot of bikes (my 3rd bike: 2002 R6) get beat up on in 2nd gear, and it is the first gear to go bad. 2nd gear is a popular gear because it produces a good amount of torque for wheelies, and is not overly torque like 1st gear. So a lot of people like to punch it into 2nd hard, or wheelie in 2nd...resulting in slipage. Slipage will feel like the bike is having hesitation problems.....like the injectors are sputtering...but its not the injectors, it the clutch slipping because the gears are all fucked up. The bike will "buck" or jerk back and forth when you punch it if there is a problem with the gear. You may want to look out for this feeling in 3rd gear as well.

When you finish the test drive, let it sit to examine any leaking fluids under the bike.

The biggest thing to look out for is that 2nd gear tranny problem. Its the biggest pain in the ass to deal with, and its costly to fix.