Originally Posted by supcom
Riding in the rain without protection in 70 deg weather would be a miserable experience. This assumes that the temperature does not fall when the rain begins coming down. The issue is not staying dry, because unless you use a bike poncho and have full fenders,, you are going to be wet. Even with the best rain jacket and pants, you will be soaked from sweat 15 minutes after you put on the rain suit.
Even though you will be wet, the rain suit keeps the cold rain off of you so you stay warm. You won;t be the most comfortable, but it's better than no rain gear.
Don't forget rain protection for your head. A $1 shower cap will cover your helmet and give you total protection there. Put your feet in plastic bags and tuck the top of the bag into your rain pants. You can buy waterproof socks, but the bags are cheaper. You might also consider latex gloves.
I'd say this might be a personal thing for each rider to decide. After all, Supcom here I'm sure has figured out what he likes. But my experience is totally different. I'll ride in the high 50s without a waterproof rain jacket (unless it is windy, then it comes on). In the 50s and upwards, I just wear something that keeps me warm when wet, like a short sleeve wool jersey or maybe a light breathable nylon windbreaker. That's not to say anyone else is wrong for advising anything else - it just seems to be an individual preference. I know my wife shares the same preference as me. I prefer rain wet to hot sweat wet.