I was doing some more research before I pulled the trigger on FG400. I came across a direct comparison between M105 and FG400. The testing was done by Todd Helme of Autopia-carcare. The review/testing was EXCELLENT!!!! I HIGHLY respect Todd's opinion.
The testing was done with a rotary and DA polisher. The results were completely opposite of what I expected. FG400 slightly out cut M105(except with MF pads), while M105 finished slighty better(except with a finishing pad) than FG400!!! In 4 of the 5 tests, M105 finished better than FG400. So, as far as FINISHING ability for the most part in this test, SMAT > DAT.
I'm no longer going to buy FG400. Not saying FG400 is bad, I just prefer a better finish, even if there's a bit less cut. Plus, I like to use MF pads and FG400 didn't fare so well with them.