sloping tob tubes are no problem per se, what IS a problem is the clearance that your front triangle provides. in order to rack the bike on the innermost mount, you'll have to slot both arms through the front triangle (assuming no adapter). bear in mind this includes the little flat things protruding from the bottom of both arms that are supposed to lie flat with your seattube/seatpost (you'll know what i mean when you see it). most all rear suspension bikes use a lot of space in the front triangle, and jump/trials bikes will have too narrow a space because the top tube is so close to parrallel with the down tube!

no limitations i've encountered as yet, going at 90-100kph seems ok so long as everything's secured (REAL) tightly. Not sure how to lock the rack to the car though, still havent done that yet.