No, I wouldn't. If I released a Bitcoin client that looked like it was hashing twice as many hashes, but actually wasn't, and also donated 5 bitcoins out of every block of received bitcoins, would you run it? If you have such code, just release it. It will strengthen the network and promote the adoption of a version of the client with other improvements besides your improvement. If you really did release code that doubles the hash speed, I'd be more than happy to donate at least 5 bitcoins to you. Actually, probably more than 5, but I'm not sure how many.

Interesting replies.

I don't have such a client -- just to clear that up.

What I'm getting at is this:  If BTC were highly valued, and a very clever-but-selfish developer had an exceedingly fast client (say, someone gets CUDU running on all cylinders, or hand-crafts SSSE3 for i7), would they be better off retaining the program for their exclusive use (during inflation), or offering it for 'sale' by effectively charging a fee for every find.

I suspected it would be more profitable to distribute it with a small fee, but the reception sounds a bit... less favorable.

doubling the hashspeed would double the expected value for generated bitcoins in a certain time.
as long as:
expected value  - tax = higher than the expected value before doubling the hashspeed (without taxes),
I guess I'd use it.

But it would go up less if you were the one with the fast client and everyone else had "normal" clients. If you distributed such a fast client to everyone, then yes, the benefit would cancel out.