If I didn't ride when it was hot/humid, half the summer would be gone. I did have to build up to being able to do this, and I still don't love it. Most likely, on Wed.-Friday of this coming week, I will ride very early in the AM (5-6). I'd rather get a 15 or 20 mile ride in at this time, than suffer just to get more miles. I used to actually go a spin class on those kinds of days, many years ago, when I started riding, but I would not do that now. I either go out early, take a rest day, or go running in the woods. I have a lot of really shady, short rides I can do when it is hot out. The thing is, that this kind of weather never lasts more than 3 days here, so it's not like I am in Florida or Texas.
I've ridden in the Blackstone Valley area, but not on the Bikeway. We did a tour across MA a few years ago, and that area was a big part of it.