I've just replumbed my cooling system with an 82C PRRT that came with my new engine. From my limited experience with it running in the donor car, it seemed to hold temperature steady. The plumbing was very easy, with just a few cuts of (silicone) hoses, and a new section of hose and handful of Jubilee clips to buy. I was going to do my own pikey QED-style remote stat mod by putting a standard stat housing in the top hose and removing the centre of the stat in the standard location, but several people have said to me that the coolant temp can "cycle" as it warms up. No such issues with a PRRT, apparently. Plus it came with the new engine, so made sense to just use it.