I figure you're probably already aware of these Sean but thought I'd mention it just incase.
Was tinkering with the mod today just for laughs and noticed a few ultimate spells so busted out the cheat client to give a couple a whirl. Ran into a couple issues.
Diluvium - causes some pretty serious client chugging when cast, talk about drowning everything in the remote vicinity though yeesh ._. Units whose tiles have been turned to water (AI) just end up standing on water. Quite odd to watch.
Great Flood/The Oncoming Storm - client locks up when you click cast spell on these. Seems to show most targets as invalid. Wasn't actually able to make it cast in the end.
Omen of Astaroth - No delay issues but shows all targets as protected from hostile spells
Strip Mountain - Seems to work mostly though I have yet to see any resources pop out from the ones I tested.
Break Realm - Guessing this is meant to be ridiculous with that crazy mana cost. Talk about turning everything into bananas, floating rivers and resources popping out of the side everywhere ._.
Tested on an i7 @ 3.85GHz, Nvidia GTX 480s.