Stats to MT Gruul's/Mag?

I tried searching and failed, but I'm wondering what kind of stats I should be looking for to be able to MT Gruul's and Mag (mainly because it seems my GL doesn't exactly have much faith in me yet, and I want to hurry up and shut down all his doubts or whatever issues it is that he has). I read somewhere that 250-300 SD is good, but I couldn't find anything on unbuffed HP goals or suggestions. I'm currently sitting at just about 12.5k unbuffed (I got happy when I cracked 15k fully buffed...lol).
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I got into a pug the other day just tanked the priest on high king ran out of mana and the healer fell asleep so give that a go, then the tank on high king died and i picked him up lasted bout a minute which i thought was pretty good they said next time come with 14k unbuffed, and i'd say 300+sd would be fine, i didint have any troubles with 223 (they were killing my target first) but dps was holding back a bit.
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Especially on Gruul I don't think 12,5K health and 250-300 spelldamage will be enough. Gruul is basicly a dps race, so you need to put out as much threat as possible to make sure the dps doesn't have to hold back. Also because of the silence, there is a chance you could recieve a crushing blow if it prevents you from casting holy shield. Especially further in the fight, those silences can be deadly if you have a low healthpool like that. Magtheridon has a nastly cleave that can deal massive damage as well, but the threat there usually is less of an issue, because he is a demon and (for our guild anyway) you have a little bit of time to get a nice headstart because of 1 maybe 2 remaining adds when he becomes active.
Unfortunately I can't give you any min. stats that should be enough. Also I think it strongly depends on how well geared your raidmembers are. But to be honest, I don't think you're at the point of tanking those bosses yet if you have 12,5 K health and 250-300 spelldamage. Correct me if anybody thinks I'm wrong.