Steve, definitely be prepared for cold, wet, and snow this time of season. That can happen in any month of the year on Whitney, but it's especially important during the transitional months of Sep/Oct. Your pack may be heavier than you'd like, but you know the old adage: fail to plan, plan to fail. People die on this mountain virtually every year, often because just one thing went wrong that they weren't prepared for. There have already been two fall-related fatalities just this summer, both in relatively good weather conditions. Many others get in serious trouble when weather catches them unprepared. Inyo SAR stays quite busy on Whitney.
Based on the resume of peaks you mentioned, expect this to be another few notches higher on both the difficulty and misery scales. The best way to breeze through this hike is to be prepared not to, if that makes sense. It's not technical in any way, just a walk-up, but by all accounts it's one of the most difficult walk-ups in the country, even when the weather is fine. As I pointed out earlier, you spend a lot of time between 13K' and 14.5K' on this hike, and that's just not the case on most typical fourteeners. If you had a headache at 11K' on Gorgonio, expect much worse at 13K' and higher unless you can acclimate well or have Diamox in your system.
Not trying to rain on your parade, just pointing out some truths for consideration from personal experience. When I first attempted Whitney a few years ago, I underestimated badly. I had a few Colorado fourteeners under my belt, and quite a number of 10-12K' peaks as well from the Rockies, Sierra, and Cascades. I figured Whitney would just be a little longer version of what I was used to. I had minimal acclimation and was motoring along pretty strongly the first 6 miles. But by the time I was at 13K' on the switchbacks the only case of AMS I've ever experienced hit me like a ton of bricks. I'm not kidding when I say those were absolutely the worst hours of my life, trying to get back down safely (and solo). And I'm not saying that lightly, considering I once spent several hours dangling in a climbing harness 400 feet above the ground on Cathedral Peak with a useless, injured shoulder. I was much more confident I'd get down safely from that technical climb than I was about descending 8 miles on Whitney's walk-up trail with full-blown AMS.
Anyway, your posts remind me very much of my mindset before I tried Whitney the first time. My point is simply, take this mountain seriously. It's not Baldy or one of the Sannys, especially this time of year. Be prepared, be safe, and best of luck.
