For your tank Chuck, if you've been happy with your AquaClear filters then I totally agree with Blair, I would just go with AC-110's.
IMO they are 10-fold better than Emperor 400's. I wouldn't take a brand new Emp 400 for free, but that's my experience with both brands. And as I already stated, if you've been satisfied with the AC-70's, just go up in size and stay happy.
Also, you already know the workings of the AC's and how easy they are to maintain. The 110's are identical to the 70's except for size. Everything goes together the same way.