The 8520 and the 8520 would both be a big step up from the 8100. But it's also not the best there is if your looking for the fastest. Though it is a quick light thing, I do enjoy mine.
Based on your questions, I suggest you go to
Smartphones, Cell Phones & Smart Phones at BlackBerry.com and click the button that says Smartphones, then click Compare Smartphones. Handy tool that allows you to drag and drop different models and compare the technical specs.