I believe it's 10mana/int below 200 and 5mana/int above (at level 60?).  I've always gone for cha first and int/mana/hp/ac second, under the assumption that it benefits not only charming but mez resists as well (fewer resists = less necessity for hps and shit anyway).  Plus, stacking Berserker Spirit and Rune V is like an extra 1k hp or so buffer (more when I get Bedlam, the level 58 version of BS), so I never really cared about losing 10dex and 14cha (pair of electrum star ruby rings) for 110hp and 10ac (fighting 50+ mobs, that gives you what, an extra 2/3 of a mob's melee?).  Also, I'm operating under the assumption that more dex = regain your concentration and continue casting.  I could be dead wrong about cha affecting mez resists, and dex affecting channeling, but at 251 cha I notice almost no difference between pre and post nerf charming, as long as I restrict myself to high 40s/low 50s mobs.  I've been soloing north and west wing of HS easily with charm.  Zol knights (the weakest mobs in seb) hold full duration for me, and some still con db.  I did a hate run the other night and held clerics as pets fairly well (with malo though), had a few quick breaks within a minute or two, but for the most part I was getting several minutes per charm (though full duration only once or twice).  In summary, I am a cha whore.  I will always want my cha to be as close to 255 as possible without going over, after which I'll take whatever involves the most int/mana/hp/ac/dex/agi (more assumptions, this time that higher agi = more dodge - and I do wear Insidious Slippers over GEBs).  Just keep refreshing that Berserker Spirit, your Rune V should get eaten just a little bit at a time (I've actually had it last the full 110 mins or whatever a few times), and hp gear won't really matter much. 
 
Edit - currently I'm at level 59, probably makes a big difference compared to the level 55/56 guy charming in HS. 
		
		
		
		
		
			
		
		
		
		
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