The condensor efficiency will have a minimal effect, in other words there is little difference in the most and least efficient condensors. It's capacity that counts, and that can only be significantly changed by putting in a larger condensor.
When changing over my 240D I put in the R134a expansion valve. Later on it started leaking and I replaced it with a new R12 unit that I had laying around. I could tell no difference in the two. I expect that the R134 actuates at a slightly higher pressure.