My memory is foggy, but one method of updscaling defaults to whatever project resolution you have set to upscale, the other lets you choose up to 4x upscaling... so technically in this mode you can upscale higher than 4x by setting the project settings higher. Unfortunately, I don't remember exactly how to enable the other mode... as a media level effect, vs. event, perhaps?
wow, I didn't know that, there are media effects, I've been using vegas for a long time, but I'm just now getting into it, I didn't even know that, because I never needed to use it before hehe