When I installed FSX-SE, it chose ULTRA settings for my computer, and with no addons whatsoever, I was getting better frame rates than I ever remember  seeing from a straight out install of FSX and Acceleration! It does seem better, but I could be imagining it. :-/

The talk in the Steam Forums is that it does seem to perform better than FSX Standard/Deluxe with Acceleration, or FSX Gold (which is what it is only on Steam). People are saying that "this product", or "that product" does/doesn't work, but unless you really know what your doing when it comes to porting them over, it can easily end up being a miss instead of a hit.

I can imagine the creators of the FSX to P3D Migration Tool rushing to make a migration tool for FSX to FSX for Steam! :D ;D