I've always used Shimano M520 pedals on my fixed gear bikes. Lately, one of the pedals un-clips at the most inopportune moments despite being tightened down to the max. So now it looks like it's time to replace them (the cleats are new). Having said that, I've heard good things about Time Atac pedals and have been curious about trying them. Does anyone have any thoughts on them, and which model to start with? Or any suggestions for other clipless pedals, for fixed gear (street) riding? I guess I'm just ready to try something different.

Thanks.