If you're going with a single pump for a tank that size I'd definitely go external, less heat transfer to the tank... Those mag's, especially in that size, run HOT...
(I do things differently, instead of one big pump (And a single point of failure) I have two smaller submersible pumps, one returning to each side of my tank... (Quiet One 4000's)... That way when (These are mechanical, it's not if, it's when!) one fails I'm not in 911 panic mode, the tank's still getting turnover and I can casually fix/replace it...