For Epic casting rethink what you're using it for, It's real game-breakingly overpoweredness is when you work up stuff with stacked reductions in spellcraft DC outside of combat and either make permenant changes to yourself/environment or even better instantaneous ones.
Check out the candlekeep conpendium online, the one with Shaaan the serpent queen for a suitably cheesey use, she built a permenant spellward for herself that relects all targetted spells of 9th level and below, it can't be dispelled by less than epic magic and it never runs out of turning. She effectively made herself immune to direct castings, and picked up a reputation for being unbelievably hard in mage duels. If that doesn't appeal try specing up a "Create Minion" spell that turns a cabbage into an uber-monster totally loyal to you, make it's effects permenant and then spam that for a few days. Spells like the hellball and epic time duplicate are frankly rubbish compared to what metamagic can give you so don't try to use them in a fight. but the backlash and +10 minutes to casting and even the xp costs are all fine on long duration buffs that you can set or contingent effects to keep you safe.
If SR is troubling you write up an epic spell that degrades SR of all hostile critters within a set distance of you, over a period of X rounds they accrue minusses to SR until it's eaten, that shouldn't even be that high a power.
Make sure you read through the LNG to batman builds, it's all appropriate only more so, go for the cripple shot not the hp kill.