shimano all the way...if you cant swing 105s, which is what your 520 should have origionally anyways, go with Tiagra...they'll do just fine. MTB gearing...all you need to do is for your crankset, get 3 rings vice 2...gives you much lower gearing for those loaded climbs up Mt. Kilawea, or whatever other big inclines you have ahead of you. What did you have origionally? Have fun!