Hey and welcome to the community
I have had some experience. Mixing in some Sony Alpha lenses and Canon on a NEX-5 but the results should be somewhat similar to what you may expect.
First to start with the Sony lenses. I am using the SAL35F18 and the SAL85F28 on the LA-EA1 adaptor (first gen). The results overall were great, even wide open, my shots and videos were impressively sharp. What I did need to consider is that the autofocus system was not going to be as fast as the electronic focus from the dedicated E-mount lenses so there were tendancies for it to hunt before finally nailing the focus. Manual focus removed that problem.
Personally I would have and may still do, keep the lenses and purchase the LA-EA2 which is a little more pricey but packs a punch when coming to autofocus. Much quicker and much more accurate. For video work, I would say this would be worth it
The EF Canon lenses, well it was all manual with no aperture control so everything was wide open. The photos were great but when recording video, I had to be very careful since I was aound f1.4 or f1.8. I could have just found some old manual aperture lenses but I rather not have the same focal lenses in my camera bag.
Your VG20 would have a more intelligent autofocus system so your results may be better but not sure by how much using the same gear as I.
If there are any tests, by all means, let me know and I will do what I can to help out.
Regards
