I finally had the time to sit down and get the problems I was having sorted out. One apparently was the DJI F450 frame and its built in power distribution board confusing the mag, the other appears to have been a bad motor and/or ESC. Once I moved everything over to another frame things got a lot better but I was still having stability problems with level, altitude, and position hold. I noticed that it seemed to be down on power and didn't sound like the motors were maintaining an even speed. At that point I swapped out both the motors and ESCs for a set that I know are good and that I usually use for testing purposes on larger frames. Once I did that the stability got a LOT better and there was just a bit of oscillation that needed to be addressed, that was taken care of by trying some different props until I found the best balance between stability and performance, currently a set of Graupner 10 x 5.
I did some tuning of the parameters and made a GPS shield from some copperclad circuit board I use to make FPV antennas and by late Friday had it to the point that the autolevel was working well along with altitude hold and position hold. I was planning a trip to the flying field to do some FPV flying with my TBS Discovery quads Sunday morning so I rummaged through the parts boxes and came up with a CMOS FPV camera and I borrowed the Immersion 600 mw video TX from my Cinestar, both of which I mounted to the Mutliwii frame. A quick test in the backyard to make sure that the vtx didn't interfere with the GPS reception and it was ready to go.
First thing I did at the field was a LOS test flight to make sure everything was working right. GPS position hold was working quite well just being pushed around a bit by the wind so I decided to try RTH and it worked, returning to within a couple feet of where the board was armed. RTH was very SLOW trying to move against the wind but that's something that can be tuned so not a big deal, the important thing was that it did come back to the home position.
It was a bit twitchy in the wind and unfortunately I couldn't make any changes to the settings as my netbook refused to run the Multiwii config program, works fine on the big laptop but refuses to run on the little one! This morning I reset all the parameters and did a little fine tuning and it's much smoother yet again, just need to tweak the position hold and yaw a little, otherwise it appears to be flying quite well.
The third picture above is the quad parked in altitude hold and position hold in the front yard, next time I have a chance to get out to a field to fly I'll bring the video camera and get some video of it doing its thing.