What I was getting at is the 590 will make great power down low, and you won't have to shift higher than 6200. It will however, have a rough idle. How close do you think you are on all other aspects of your combo? Jetting? timing? Cold air intake? 60 ft? Maybe a post on your entire combo, along with shift points, and all details of the time slips is a good idea. There may be some gains to uncover, which will help in deciding just how much cam you need to obtain your goals. With as loose a converter as you have, you can get away with about anything though.