You'll gain it if you use alloy 44 inner shafts. I don't think spicer 30 spline shafts are stronger than an alloy 27 spline.
Think of it this way though. Your chances of losing a R&P aren't that high, if you know your swapping it who cares about the housing, and your current shafts should get you by. Nice thing about the 30 shafts is they are easy to change.
I've gone the route of making things work temporarily and ended up wasting to much time, effort, and cash on the whole deal. The adapter isn't that bad of an idea, but I personally wouldn't waste the time. Think of the ground clearance advantage you'll have with the 30.