Difference between 520 and 525 is 520 has 20mm (0.78 inch) thickness and 525 has 25mm (0.98 inch)thickness.
I recommend you to do not change the number of teeth in front sprocket. If for any reasone you want to reduce the speed and have more torqe on your rear wheel, do the changing on rear one. 17t to 16t does make difference on riding. However i recommend you do the edit in the back becasue it last longer. Instead of changing front from 17t to 16t and have the back at 39t, keep the front 17t and change the rear sprocket to 41t (the Ratio of them are simlilar).
I wish you good luck!
Last edited by ShervinRRR; 04-13-2010 at 07:39 AM.