Or access your online banking if you use it,
or online credit card payment,
or your email accounts that may provide them with enough personal details to commit identity fraud
You could also be making every single file stored on your computer available to a bloke sitting in a room on Korea, again providing them with enough details to clone your identity.
The idea of "my computer runs fast so it can't be infected" is ludicrous, do you seriously think that the people that write the really harmful stuff would make it so obvious you have a problem, they will be writing it to hide itself as well as it possibly can and this would include using as few system resources as possible.