I'm planning to get a new set of mountain SPDs for my road bike. My current ones are M747s (circa 1994) and they've been a great pedal, but now I have to douse them in White Lightning every other ride to keep them quiet.

I've heard that the SPD-compatible third party brands are to be avoided (is that good advice?), so here's what I'm considering:

Shimano M520, ~ $50
Shimano M540, ~ $90
Shimano M770 (XT), ~ $110

Can anyone tell me about the relative quality between these models? If the main differences are off-road durability and mud shedding capability, obviously I could care less about that and will go for the cheaper goods. The weight differences are so small as to be negligible IMO. What I care about the most is long-term reliability and consistent cleat retention/release.

Scott