In the grand scheme scheme of things having the MRCS (even if done super early like F1 or F2) does not help a great deal. The reasons being:
- they don't know what it is and you will most likely have to explain how this is an achievement
- the MRCS will be listed in a very small section at the end of your application, thus it might get missed
- it takes a lot of effort to pass both parts. This time might be better invested by studying for the USMLEs and do research
I did it and went through the whole match process. Unless I brought it up, I doubt that it would have been noticed.
Hope this helps