I replaced my SPDs with Time ATACs ages ago and have never looked back. It was easily one of the best things I've done. No more mud clogged pedals (made for several long rides home), no more self-disassembling pedals (made for one really long ride home) and plenty of float keeps the knees happy. I've had to replace the springs in 1 pedal after ~35,000 miles, otherwise I don't touch them. I have ATACs on everything I ride, road or mountain. I haven't found anything else that works as well.