P (being a winning player)

[ThinkQuick]

Just wanted to check this:

I have a person's hourly rate (which is negative) and hourly SD.
Is calculating the probability that he is greater than a 1.0BB/hr player as simple as setting up a standard curve with Mean = hourly avg and SD = SD, and finding the area above 1BB?

i.e. -1BB average with SD = 9BB: Area above 1.0 = 0.412..

so there is a 41.2% chance that this player is a >1.0BB / hr player.

Also, how valid (if at all) would stats like this be with such a large SD - only 500 hrs of B&M have been played.