I didn't benchmark frames before and after, but I would swear I picked up a substantial boost. I'm now getting in the 60's for FSX frames and a solid 75 on timewarped at Bowerman (Orbx scenery) in a Flight Sim Developers P-38. In the stock 172 I'm getting between 115 and 130 depending where I am looking on FSX frames.
I don't have an explanation but the battery switch direction in the Flight Sim Developers P-38 is apparently reversed. Took me a bit to figure that one out and be able to start the engines in a saved scenario, but everything else seems fine.
The beta didn't fix the issue with joysticks losing focus if you do anything outside of FSX, though. I fired up my browser to write this and just checked and joystick seems dead. But this is how it was for me before going beta.
Lots of "is it ok to run" this or that dll when you fire up. FSX must see all the changes. And FlyInside also wanted to know which video card to use, but all in all no real problems.
If anyone else sees reversed switches in other planes, I would be interested to hear. I don't think I've had it wrong all this time as I've started the engines from cold a bunch of times in the '38. But maybe I did. Magnifier would be handy here as I could read the writing.
Edit...
For whatever reason, now the battery switch in the 38 is fine after I restarted FSX. Also, and Orbx people may or may not care, but each time you launch the beta FSX it turns out it asks you if you want to run various scenery .dll files - mostly the object flow ones. It tells you they aren't tested to work (seem to work fine) and asks you if you want to run them just this once. No option to just accept them for all time like the various FSX and airplane .dll files. So it nags and the level of nag depends on how many of the various object flow .dll files you have. Might be able to turn off object flow in the Orbx control panels but I don't have time to experiment right now as lightning and thunder are here and I need to power the rig down. Now that Dovetail has announced joint scenery offerings with Orbx, I bet this gets sorted pretty quick. But for now, you get nagged.
Also, frame rate increases aren't as dramatic in Honolulu but there is a lot of scenery there. It was down in the 74-75 timewarp fps and 46-47 FSX fps there for me.
All in all - success! I'd say go for it.