Another nod to Aerostich R3 here:
I have one (look at my avatar) - incredible protection and very versatile. 100% waterproof when all the vents are zipped up. However, in a real soaker, water does have a way of migrating into the suit from the neck area. There is a collar that you can raise and close with velcro that will protect almost all of your neck. However, water will still hit your exposed skin on your neck between the top of the collar and the bottom of your helmet, and then trickle down behind the collar. The tiny trickle will seep down your neck and eventually make contact with your shirt, where it will then wick down into your chest area. After enough time, in a really heavy downpour, you may end up with a damp neck area on your shirt. But the rest of you will be bone dry underneath the suit. Been there, done that.
Your wrists may be another entry point for water unless you wear some waterproof gauntlet type glove covers:
It is possible to enjoy warm, dry hands while being plastered and hammered and hosed. Made from 3.5 oz/sq yd 40d 3 layer breathable-waterproof ripstop nylon. The thin ripstop nylon laminated fabric breathes enough during rain conditions so your skin won’t become clammy. The oversize gauntlets...
www.aerostich.com
The R3 suit vents and breathes incredibly well in the heat. When it heats up, fold down the collar and zip open the vents. Air will enter through the wrist and collar openings, circulate through the suit, and then exit out the armpit and back vents. It really works very well. I use it here in our hot Texas summers (well over 100°F)! You don't want it to be skin-tight so that the air has room to circulate. It will
inflate a bit from the incoming air pressure and that really helps to cool you.
If you buy one, get it one size too big so that it breathes better in the heat, and allows you to layer up in the cold.
Just my $0.02, as always, YMMV.