Never own the F3.5 so can't compare. Anyhow the F3.5 goes only 1:2. Colour and contrast of F2.8 macro is :thumbsup: compared to 50/1.7 and 50/1.4 (all three are very sharp lens)
If anyone have a F3.5, maybe we can organise a session for a shootout of the 50mm. I still have the F1.4 and F2.8
For the 50mm Macro the main difference of RS and non-RS is the focus limit switch and circular aperature. Desirable features to have.
One concern is the RS contains rubbery material on the lens body and focus ring. I have the feeling that these materials will degrade over time. The rubber on my friend's 24-105 seems to feel a little funny (feels a little harder and colour turning darker) after about 5 yrs. Some of the RS 50/1.7 also feels a bit funny to hold.