I find this issue intriguing. The only way to get a solid answer is to pull your engine and put it on an engine dyno. Who's going to spend the money to do that? Not me!
So, here is my take. My LS3 M6's stock baseline done for my cam/bolt-on package was 378 RWHP and the finished product two days later on the same dyno was 461 RWHP which equals a 22% increase in RWHP. By my logic the engine crank HP must have went up by the same amount - right? So then my engine crank HP went up 94 HP (426 + 22% more). Thus it is about 520 HP. If I use the conventional 15% driveline loss for a manual tranny my HP would be 540 HP (461/.85).
Which is right? Who knows? Like most things in life the answer probably lies somewhere in the middle.