The crashes do not happen regularly, though they occur often. The "atidxx64.dll"-related crash ("Faulting module name: atidxx64.dll,", seen in Event Viewer) happens during gameplay, while the other crash happens much less often while I'm loading into online. Both of these crashes have only occurred during online play, though I have not tested them in singleplayer.
I run a pirated copy of windows 8.1, a 280x on 15.6 beta drivers (as per a suggestion on another forum) and an i7.
When the game crashes, windows gives me the "GTA5.exe has stopped working, etc." popup.
Could you help me fix these issues? I will try to supply any extra information if required, as soon as I can.