The people I'd heard were in the tyre trade (doesn't meant much), and also mechanics etc so not S3 or BM owners I guess you learn something every day. It just goes against basic logic to me! They're the tyres doing most of the work. I guess ideally though, you'd have 4 of the same all round and rotate often. I've never had a road tyre suddenly "let go" though. Usually, even on the rear, you get plenty of warning. Slicks and semi's will break away quicker from my experience but obviously take longer to get to those limits. I guess it's down to preference and driver skill. Understeer being deemed "safer" to control to most. As I've heard mentioned before "understeer scares the driver, oversteer scares the passengers"!