Benchmade's limited edition M390 steel is treated by them which may cause a variance of performance between makers, but M390 is reportedly very similar to Duratech 20CV and IMO, not that big of a deal as compared to their D2 which IMO (again) is treated quite well and is a real performer.
I wouldn't spend the addtl. $$ for the M390 unless I could justify it and I don't think it can be justified except for those who dig using new steels as part of their knife collecting hobby which is cool and part of our knife hobby.
I'd reccomend that for normal use the current production model BM 710 D2 is all the blade steel you'd need in this model.