I have heard the 32500 cap for Spell/Physical Resist before but don't know the formula myself (i think its 650 resist blocks 1% of damage, caped at 50%). I also think that going over can cancel out someone else's penetration. For instance, if they have 650 spell penetration and you have 33150 spell resist you should still be maxed out (50%). However, I have not run these numbers myself and would be interested if anyone else has more insight.