As a general rule with respect to JT's early post about jumps being splinters except when they're not splinters and so on and so forth, a decent general rule is that if it's one level higher than a forcing natural bid, it's a splinter. So, e.g.: 1♣-1♠; 2♦ would be a forcing diamond call (reverse); so 1♣-1♠; 3♦ is a splinter. With respect to the initial hand, I certainly wouldn't open as south. I would also take a call over 4♠. Partner is willing to play in game opposite 6 points and 4 spades; I've got a great 5-card suit, 9 HCP, and a singleton. I realize that the singleton king isn't necessarily pulling its weight, but it's still a monster hand in excess of what I've promised for a 1-level response. In losing trick count terms, I've promised a 9-loser hand, and I have a 7-loser hand, or roughly the equivalent in playing strength of an opening hand, now that we've established a fit, particuarly a 9-card fit. I'd cuebid my second round control with 5♦ over 4♠. Sometimes you'll stop short of slam and make 5, just as you would have had you passed out 4♠. The relevant cases are where you miss a slam, or when you get too high. I think the first danger is more likely than the second.