LM vs LM-R is a toss-up IMO (in 20" size) but since you already have the LM-R's it's a no-brainer - keep them. Now if you were asking about the same wheels in 19", I would vote for LM's because they are available in better sizes (width / offset).
'08 E90 M3 - Alpine White - Sold
'13 E92 M3 - Silverstone II - Sold
'04 E46 M3 - Jet Black - BBS E88, KW Clubsports, Brembo BBK, SuperSprint Exhaust