hehe, as skyther pointed out in another board, this is based on his own experience. And my own early tests (using SS as I don't have a Hi-MD) tend to confirm that SP still sounds a bit better than Hi-SP.
I intend to do a full ABX test involving Hi-SP (recorded with Sonicstage), Type-R SP (I can digitally record from my deck to my PC) and others competitors such as Lame, MPC and Vorbis, at high quality settings. Such a test has never been done I believe, it could be interesting.