Oh, Dark_Mark, i'm really sorry, but i thought that Venom's texture was 1024x1024, but i only noticed right now that it is 512x512, his texture looks all the same, so i got a little confused.
Teancum, i checked right now and Gambit's mannequin is 256x256, and it worked on the xbox.
so this means that 256x256 is the limit, and it is a little bit obvious since all IGBs on the XBOX are 256x256, but for the boltons, any settings seems to work, even DXT1 and 512x512.