I don't think south's 3♠ invites slam, it just shows a side suit and forces game - north could be 4-3 in the majors, and then 4♠ would probably play better. North's got too much offensive strenght to double 5♣, but not enough to venture the 5-level IMO. Thus a forcing pass is the correct call. South should double this, not being able to underwrite a contract of 5M. Btw, I can't see how 5♥ could be a make, with a loser in every suit except ♣s. Edit: Sorry, I misconstrued the bidding. South should double 5♣ and north should then pass IMO.