sausage said..
I had been rigging my 10m tr-8 with a loft 490 100% SDM (constant curve) and 40cm extension successfully (until it snapped last week) contrary to specs req. 520 hard top. Tested it with an old 490 soft top tushingham 100% on weekend successfully to my surprise. Maybe the shorter mast longer extension compensates - can't quite remember whether using shorter mast than specified makes it stiffer or softer?
The Loft mast may have a similar stiffness in the bottom to the next size up hard top.
I had a similar experience with an NP 400 in an Ezzy Infinity 6.0. It was sweet - too soft in the top but it didn't seem to matter and just the right stiffness where it counts. Of course that wasn't a race sail.