I ran the avi's through Registax with the same parameters and measured Saturn's disc size in Photoshop averaging the result with both X and Y axis pixel count in the formula. Here are the results of the test runs:
C9,25+Ultima 2x @ 0mm = f/21,8
C9,25+Ultima 2x @ 10mm = f/22,4
C9,25+Ultima 2x @ 20mm = f/22,45 (...which is odd!)
C9,25+GSO 2.5x @ 0mm = f/21,1
C9,25+GSO 2.5x @ 0mm = f/21,7
C9,25+GSO 2.5x @ 0mm = f/21,5 (...which is even more odd!)
Conclusion? ...well it seems that the GSO 2.5x Barlow doesnt seem to add that .5x extra to the Ultima. This might mean that the Ultima is a bit more powerful or the GSO is weaker than advertised, at least in my scope. I'm not sure what happened at the 20mm position for both barlows as I wasn't swapping them between runs instead I ran the Ultima at 0-10-20mm and then the GSO in the same way. After I was done with the testing I put the Ultima back in the focuser and shot a few avi's of Saturn which I will begin to process shortly. I guess the GSO will be up for sale as I can't justify keeping it & besides, I wouldn't give up on my Ultima just yet!