the octo extreme and the msx are basically the same. The msx comes with a better pinwheel and the msx machines a small section in the volute to help make room for those who mesh mod. The msx 250 is probably the best skimmer in that group. The vertex in 280 isnt a bad skimmer but the resun pumps just havent had enough time to prove if they are up to par yet.
Not sure what your budget is. Other skimmers that will work really well are the Warner Marine as 200. The K2 would work ok. It just wont cycle the same amount of water as a 2 sicce skimmer.
So with that said. their are many skimmers that will work well for you. The ATB 840 and 1050, the k2 the wm as 200, the vertex in 180, the bk gen 2 bk mini 180. all offer great performance. But again if your like the MSX 250 I am sure you will be really happy with its performance. I believe that are going to come out with a askoll pump version too.