Try race-tech's site for their suggestion on rate for your setup. I'll bet you $$ to dogturds that your query in their system comes back with something over .40.
OK..I couldn't stand it. Did it myself. Racetech says .43s!
Point is not that racetech is always right and FRP isn't. It's that different vendors/suppliers have different ideas of what works. In the end, it's your point of view that matters. If 'X' suits you, and some hotrod tuner says you must use 'Y' it's usually the former that will work best, not the latter.
There's always an opportunity to learn something new. In the above, you may indeed find that 'Y' really is a better choice if you could handle it.
Doesn't seem quite right to run .38s for a 14+stone rider.
BTW, racetech says their spring set length for the kdx is 543mm! AND a 130mm oil level! FRP doesn't like that idea, either (springs longer than oem 470s).