Killing dragonriders are even easier: 4 quick curses (level 5), one divine death (level 3). takes about 2 seconds. your only danger is if they see you 1st and get a freeze spell in on you before you can cast curse on them.
I don't want to sound rude, but actually even if dragonriders hit you with freeze you are able to cast all of the spells, so all the curse combination is still possible; don't know though if this just isn't a bug of some kind...
