My 'boil in the bag'
Altura waterproof jacket would do my head in after a few miles at most - I only use it for commuting in really heavy rain.
I find if I'm warm then being wet isn't an issue. Have done a couple of long, wet rides in March (Kinross Sportive for one) with just thermal T-shirt, jersey, and arm warmers. If I have bare arms I get cold really easily in the wet.
You'll have a much better ride on your new road bike