I modded a set of Grado SR60i's significantly a couple of years ago.
I used 3 sets of pads to find the right comfort level, and treble balance for me.
I found the stock pads bass heavy, and not that comfortable for 2+ hours.
The mid size pads were good, but it was not balanced enough for me after the bass mods I made.
I found the HUGE pads perfect.
I have since sold the phones, with all 3 pads on Head Fi (they were advertised here too).
The new owner things the stock pads are the best!
If you can find a local dealer or Head Fi meet, you could try them all and decide for yourself!