I would go for the 750. To get the most out of your 2k I would look at the 75-76F Super Sports(or the 77-8F as a second choice). They don't seem to be as "collectible" as some of the early K bikes and you should be able to find a very nice one for 2k or less. I have seen two sell here recently in the $1500 range and they were very nice turn key bikes. It would be hard to find an earlier K bike in that shape at that price, maybe a 77-8K as again they don't seem to have the "collector" thing going as strong. The benefit of the F bikes is better brakes, a bit more hp, and little better handling due to slightly revised frame geometry.