Well, I tend to disagree with you about drain because your most cost effective researchers are the salamanders @ 130 gold with holy upkeep. They have 4 RP, but really we're talking about 3 (drain 2) or 5 (magic 1). That's almost a doubling of your research and even if you do make a B line to const-6 you'll get there nearly twice as fast! You're certainly not going to be recruiting exclusively the ruinously expensive Anoninteds for your early game (the part where you're trying to scrabble up to const-6), so you're gonna be relying overwhelmingly on the poor little 3 RP guys spinning their wheels..or dumping an obscene amount of gold for a small bump up in research with your expensive mages.
At any rate, magic and growth scales are not really tied together so it's a separate decision. I don't really think you get hit all that hard on the bloodhunting, because lets face it with your only blood mages being capital only and competing with the Anointed for recruit turns you're not going to be doing massive amounts of bloodhunting. You only need a few provinces to hunt in, I find its not hard at all to balance a death scale with a modest blood economy.
But, as you say its all a matter of preference, that's just my opinion. I wouldn't discount the synergy of starving armies and blood magic though, hostile dominion + starving + blood rain = big problems even for high moral troops as soon as the agonies start dropping.
Horrors are also greatly more effective and your heat aura keeps them from really doing much if they turn on you.