Mad Bull makes two kinds of sleeves, the red and blue - they are both 60 degree which is fairly soft - and yes, at higher fps they will wear down much quicker an/or tear.
You can find them both at airsoftparts.ca and read about them in the small description - the blue actually states its supposed to be used for 350fps and lower.
During my several year long quest in hop up unit selection, i've actually read that those mad bulls cause jams and double feeding all over the place - mind you this boils down to your own user perspective and results will always vary.
Edit: My suggestion for 400fps and above - pair this bad boy with some teflon tape (if needed) and you're golden.
http://www.airsoftstore.ca/index.php...626jhvmv2l9cq7
The best investment I have ever made in airsoft is buying my own chrono because i do my own gun work. I can check things twice, thrice whatever you want.
I ALWAYS tear down my hop up units twice - once without teflon tape, once with. Sometimes it will fit sometimes it wont, not all inner barrels have the same diameter (such as the mad bull python) and some hop up sleeves are thicker than others - therefore not allowing the teflon tape and/or creating air leak.