We had microbore in our house until we extended it. We replaced all the pipe with the 15mm plastic stuff and each radiator has a single run of pipe from the main manifold to the radiator. Cause there is no joins in the pipes, it now means that any leaks are either at the radiator or the manifold. I no longer have to worry about a burst joint under the floor now.
I also bought lots of 1" insulation for the pipes ( its 1" thick all the way round - so about 2.5" in diamter in total - from screwfix IIRC )
There is no doubt that the radiators themselves are hotter ( an i've no adjusted the temp at the boiler panel ) and the whole house is hotter ... but much of that may just be down to the newer extension and insulation in the house as well as more radiators.
One important hing to calculate is whether you have enough radiator power for your rooms ( you mention single fins ). When doing the extension, I did rough calculations on sizes of radiators needed for rooms ( various info on the web about it ... doesn't need to be super exact as some make out on some web pages ). I realised that my house was under-powered by about 1/3 in terms of radiator size. It explained why the old house never got hot ... even if the heating was on for hours, it'd only get reasonably warm, never hot. Now I've upped the size of radiators, and added a second in the living room ... its soooo much warmer to the point of being hot and the house heats up within an hour.
I also realised I was only using about 1/6th of the boilers output. Its now upto about 1/2 of its output.
So, me personally:
- yes ditch microbore , i prefer 15mm stuff
- calculate radiator / room size - you might be surprised
- plenty of insulation on the pipework
- plastic stuff is fine for heating ( needs to be barrier pipe )
