I use alternate turning rules IMC, which seem to work pretty well. I ran the numbers QUITE extensively, and by baseline, they work out pretty evenly with WOTC's standard. However, they are more flexible.
Here's how it works:
Cleric rolls a turning check, which is 1d20 + CHA + cleric level + other bonuses as applicable (i.e. synergy from Knowledge religion or magical items).
Then roll the standard 2d6 turning damage. Each potentially effected undead creature within 60 ft rolls a Will save vs. turning check, with turn resistance as a bonus. Desecrate, bolstering and other similar effects provide their normal bonuses to the Will save, as well.
Greater turning (from clerics with the Sun domain, or other sources) destroys as written.
This has several effects - #1, it makes it a little more randomized, #2, it ties turn resistance into an attribute, and #3 there is a lot of room to bolster the BBEUndeadG. You can give him extra turn resistance, which is only good against turning, you can give him a higher-than-average WIS (which is great for undead evil clerics!), you can give him the Iron Will feat, or desecrate the room, or bolster him with negative energy from an evil cleric... or all of the above.
Mathematically, this seems to work out pretty well. The places where specific creatures deviate from the normal curve are, IMO, better that way anyway - some of the unintelligent or weaker undead are a little easier to turn, while some of the more powerful and strong-willed undead are not so easily turned, when compared to baseline.
A vampire or lich with evil cleric levels would be exceedingly difficult to turn, much less destroy, especially with a few rounds to prepare.
As a side note, I agree with the other comments that your guy should be pretty good at turning - that's what he does. But, if undead are a force in your game, and if they are at all intelligent, they will know that clerics like this guy exist, and plan accordingly.
That would mean that if an item like sacred armor exists, so too might unholy armor, providing a +4 to turn resistance, or some such. Quicken Turning works for evil clerics too, and becomes Quickened Bolster...
good luck!
jtb