Hey plummet a lot of surf specific TT's have lots of concave and apparently perform "beyond" their dimensions. ie the mako and the speedball. (I will know more about the Speedball l8r this week ;) thanks nige

I reckon a fairly square outline will give you more area and would negate the need for a 3stage rocker. You can round it off at the tips or even pull a north "phantom" on it and shorten the toeside rail if you really want to put some carve back. Those boards were pretty fun for big TT's
I haven't made any TT's but I make surfboards and I know that if you use concave you can increase your edge rocker and the board will still be as fast as the same size flatter board with no concave. I actually think they may be faster (ie quicker to the plane) as the water has a channel to take where as with the flat surface they sometimes feel as though they are pushing water. Also the longer flatter edges of 3stage rocker are harder to anchor at the 14kt end. Some have even said the concaves make the SBs Hydrofoil but that's a bit far out for even me to accept. The concaves definitely paddle in to waves easier IMO. For what it's worth I hope this is of some value m8.
I thought with some ABS rail you could get a cm or 2 extra width and length?