I've got a similar tablet to these (Voyo A1 Mini running the z3735d) and Skyrim was too laggy IMO at native resolution of 800p, dropping it further had good results but it didn't look anything like good enough. I expect at 1240x600 with some modding like removing clutter you could get it working fine, keep in mind that when there is a lot going on the frame rate will drop, particularly if there is any fire on screen like during the intro.
The Fallout games were very playable though, in fact I am pretty far through FO3 GotY on mine! You can edit the config to recognise more than one core on FO3. It sits in between the AMD C50/60 and the A6 1450 (closer to the A6) from personal experience, although benchmarks would have it above both.
It does run lots of games though - Burnout Paradise, Doom 3, Left4Dead, Half Life 2, Dead Island, Resident Evil 5, Tomb Raider 2013 all work fine from personal experience and Youtube videos. Obviously it's going to be an emulation beast compared to Android dongles as it doesn't need ports.