It is worth the extra work and effort to carry some warm duds wth you. Seriously, about 80-90% of the time I was wearing typical summer/fall hiking clothes, during my hike 8/10-8/14. But as soon as I got within less than apx. 1000' of the summit, it got ridiculously cold. I wore a sweatshirt jacket over a t-shirt almost the whole way up, but as soon as I got close to the summit, the chill in the air was noticeable and significant. It felt like February. Sunshine turned to gray ominous-looking clouds. I pulled my down coat out of my day pack and was glad I had bothered to tote it along.
I talked to a US Forest Service Patrol Ranger at Trail Camp the night before I summited, who told me he had met hikers on the trail who turned back in the last lap of the climb to the summit, because it had gotten much colder than they expected to and they weren't prepared.
I carried an old-school sleeping bag which is hard to rate by today's standards. Perhaps it was rated for fall weather at the most, but definitely not winter-rated. Either way, I was not what I would call "comfortable" the night before I summited (at Trail Camp), and I thought I was well-read and knew what I was doing. Hence, what I am suggesting is that it is worth every extra effort you make to carry some warm clothes and bedding along with you, even if you only wear them a small percentage of the time. I was in Lone Pine less than 24 hours from the time I summited, and it was shocking to me how drastically different the temperatures were; the summit felt like February whereas the town most definitely felt like August.
Just my two cents. Hope this helps. Good luck with your hike!
In this lifetime we cannot do great things. We can only do small things with great love. ~Mother Theresa
