Really good result for that focal length with the 120 mc.
I have tried a couple of times with the same camera and 5x barlow on my 180mm mak cass at 14000mm with without any success, the frame rate is just to slow. I agree with the 2x barlow being the max. I find that keeping the wavelet adjustment to a minimum works best, if the data is good you shouldn't need too much processing to start of with.