[Poll] Frost Giant Vampire Stronghold Level? (Patreon)

Hey all!

Today, I'm breaking ground finally on my big fat Vampire Stronghold adventure. Here's the image:

As always, thanks to the total bad-ass Dyson Logos for this crazy huge map. I know the bad guy will be the frost giant vampire lord (CR 21), which means this sucker is going to be high level. That's right—fourth tier!

But how high of a level? 

Let me know below! I should start this afternoon sometime.