Most 520's I seen had LX cranks with 44-32-22 rings. If you have a square taper BB one step down to Deore cranks will be just about as good and cheaper. I started out with Deore and LX derailleurs and when they wore out upgraded to XT. The XT is more solid, much smoother shifting and appears to be wearing better. 11-34 is the best cassette and not just for the "34" but the spacing on the last couple of cogs is better for serious loaded climbing.