I'd say depending what motors and compression your running, and the octane you 'need' to run, but I heard it drops an octane point or 2 every couple months while it sits.
Personally, I'd dump it start over. Last year dumped @175-200gals Didn't want to chance my new blower motors with 'old' fuel and that was only 5mo. old. Cost me $500 and sucked, but better than melting something and having engine builder tell me "I told you to dump it"