Mike the 250A probably matches up best with the ATB Large. I haven't done much research, but the airpull looks similar at 2200+ LPH. The price though is not so similar. $2000 plus dollars for the ATB and only $900 for the SWC. $$$ wise not really in the same category, the SWC is much more affordable. Performance would be similar, based on airdraw and body design. The base of the ATB also looks wider by a couple of inches. I would start another thread under the lighting, filtration column, specifically with this question if you want a better answer. Since this is a skimmer review thread and people that might be in the know, might miss this thread. For what its worth, there is nothing cheap about this skimmer, it skims very RICH. Right now the 250A seems to be the best working cone for the money. There are other really nice cones as well. The ATB is one of them.
Redhanded this will be an upgrade over the MSX200. Noticable improvement.