I did a same day before and after dyno with my LS6 cam install. No other mods - 32 HP increase I think.

I think 40 RWHP is very possible given you have bolt-ons to support the cam and don't mind moving your peak hp up the rpm band.

 

a member on the board mad 68 rwhp with ONLY a cam install on a stock headed, stock bottom ended ls1 THROUGH A FORD 9" with 4.56 gears....