I just noticed a very similar Roman numeral golf recently concluded at golf.shinh.org. Adjusting ySas' winning Perl solution to that game for this one produces this 58 stroker:
which has a similar form to robin's early-lead 60 stroker above -- though it uses a different algorithm. Both these solutions are very beautiful, very Perlish, and quite astonishing (at least to me).s/(M)|D/4x@-x5/eg,s/C4//,$\=y/LXVIC4/DCLXM/for(<>)x3;print
I especially enjoyed ySas' ingenious use of @- above. I've never seen @- used like that in golf before and am tempted to give it a name, "ySas' device". By way of explanation, note that adding parentheses around (M) above adds one more element to the @- array when the (parenthesized) M matches. That is, the number of items in @- is used to differentiate between a matching M (two items in @-) and a matching D (one item in @-); this fits like a glove here because one and two happen to be the required multipliers.
Update: By applying ideas from ySas' solution, we can reduce Robin's original 60-stroker:
to 58:y/DCLXVIM /4 DCLX9/,$\=s/( )?\d/9x($&+!$1)/egfor(<>)x4;print