If 2♦ ("20-23, Marmic") means 20-23 HCP then we may have a slam. Assuming partner has ♣x, then our side has 26 - 29 of the 30 HCPs in the other three suits. I see no harm in exploring a slam in a 4-3 fit. Obviously, if partner has ♣Q singleton etc, this may be more difficult. As our ♠ suit is stronger, it makes sense to bid 3♠ as a slam invite. I'd guess the OP would have a system of relays that helps determine if slam is on.