This is simply a matter of common sense. I'm sure we all agree cylinder bores and cylinder heads a are designed with fins to increase surface area to improve dissipation of heat. A rough surface has a greater surface than a smooth surface and will therefore dissipate more heat. How much more is the question. My guess is, a little more. I like the rough cast finish better anyway. Cleans up well with a scrub of 1890 formula Bon Ami. And Triumph liked the rough cast finish too - cheaper!Here we go again...
Rough cast engines run cooler than polished and a polished surface radiates less heat.
Sorry chaps, but these comments do surface regularly (and I had a guy at a bike show last weekend say the same thing to me about my engine), but no one ever produces any figures to back the statements up.
ps: Lovely engine!!!