Ha ha, I'd already tried that and couldn't measure any difference. I'd also tried losing the uc function by increasing the hash to include lower case letters, but that was a bit slower. Update: hippo suggested that while I was typing. :)

The most promising approach may be to find an alternative to:

M=>1000, D=>500, C=>100, L=>50, X=>10, V=>5, I=>1
[download]

to do the mapping. For example, 'M1000D500C100L50X10V5I1' and use a regex or something. I made a few half-hearted attempts but didn't find anything faster.

It might also be faster to remove the reduce and do the summing in another uglier way ... but reduce is so elegant I couldn't bring myself to try anything along those lines, that would be like losing an old friend. :)