I tend to be conservative, but personally, I would backpack above 8000 feet in the Sierra in October only with a good clear weather forecast and only for 3 days max - greater duration and your weather forecast starts to get dicey. If you get an early storm, and you don't have the skills to cope, you could be in trouble in the back-country. Chance are the weather will be fine, but you're pushing it. It's not random that Yosemite NP prohibits overnight parking on Tioga Pass Road starting on October 15.
Alternately, if you're heart is set on the high country in October, hike in for one day, and then do day-hikes to other locations, returning to a camp that you could high-tail it out in <10 hours if the weather gets unsettled. For example, camp at Taboos Pass and take day hikes to Lakes Basin, Arrow Peak, etc.
There was the Oct19-22 2004 "freak" storm that killed the Japanese Climbers on El Cap and resulted in multiple SAR backpacker rescues. Jim and I were on the wrong side of a class-2 pass when that freak storm hit, and it was hard work and quite stressful to extract ourselves. And there was the early October storm in 2009 that would have caused problems at altitude.