dsltrc:
difficult to say as while lenghtening the boat, I extended the mast by two meter and put a big squarehead on... meanwhile the boat got heavier than hoped for... if you would start from scratch you definitely end up with a different kind of killer (including budget) ;-)

costs: I profited from the low labour costs in China, but than you still buy all the harken hardware in the US and some original spareparts...and well, than come the sails. You probably better sell an SC20 and get an carbon ARC22 and it probably doesn't cost you that much more and it safes you so much frustration. would I change against an ARC22? only if I want to modify bows another time ;-)

hullshape: what definitely improved is the flow. the old hulls splashed like hell, the new ones significant less. boat is noticeable faster in light to medium wind but also earlier overpowered. don't think maximum speed improved noticeable... I use velocitek to track my speeds and so far didn't manage to achieve more than 19.8 while on a regular base the boat starts nosediving behaviours in the upper 17 knots.