I am always hot.  I sleep here in MD in January wearing next to nothing with the window open and a fan going. (my wife loves that...LOL)  

I sweat at the least bit of high temperatures.  When it is really hot,  you can squeegee my bald head.  The first time people see sweat literally puring off my head,  they can't believe it.  

I have a relatively expensive Frabill bibbed rainsuit.  When I put it on,  I sweat.   When I take it off,  I am soaked.  I guess it's better than being soaked be the rain,  I think...

I guess the only way I'll be able to know it really works,  is to go outside during a good rain when it is 40 degrees outside.  Even then,  if I stay out too long and start to heat up...

That is all.

I don't even take the rain gear out between mid June and Sept.  I don't mind the rain nearly as much as the sauna effect of some gear

Yep..raingear is for colder weather. 

I'm in the same boat.  I'd rather just get rained on and stay cool. 

If it is truly waterproof it will not breath very well and make you hotter than you already are.  I would gess the high end temp for me would be right around 70ish.

Think of it this way.  On the east coast humidity is usually very high which causes water proof breathable fabrics to well not breathe well.  Water vapor will not pass through a membrane to more water vapor basically.  When i lived out in the desert for a while i was blown back by how well my gore tex XCR breathed in a storm.  It was really unbelievable.  Hiking in a rainstorm and i was perfectly fine.  On the east coast, that wouldn't have happened.  Of course where i was living they would have humidity advisories for anything over 20%

And it is NOT true that if something is truly waterproof it will not breathe very well.  Quality waterproof breathable will absolutely breathe and will be waterproof as well.

Get some lightweight, breathable stuff for warm weather like Frog Toggs. 

I usually just wear the top part of the rainsuit, depending on the outside air temp, and how hard it is raining.

I've used Frogg Toggs for years.  They always rip and fall apart too easily.

I just use a wide-brimmed hat so my glasses and face don't get hosed.  When it's raining you're pretty much gonna get wet one way or another.  

You do need to be somewhat careful wearing frog togs, but they are my go to summer rain suit . I'm just the opposite from the original poster, in that I don't mind getting soaked from sweat on a hot day, but I'm not a fan of getting drenched from summer rain.  I nearly always carry the appropriate rain suit in the boat.

Another thing that I always do is have a change or two of clothes in the fishing truck.  I don't like driving home in sweaty clothes.   I much prefer changing in to a clean & dry set of shirt & shots prior to driving home.

Back in my lobstering days I had a trick to stay cool on hot days.

I always wore a hat.  I'd dip it in the lobster tank, bring it up full of water, and in one swift movement, put it on.  It worked great.  The ocean surface temps would get to seventy degrees in early September. 

interesting...I am also of the only cooler weather rain suit wearer...

mostly because all summer we really don't get rain per se...just severe thunderstorms and you have to just run for cover or not go out altogether.