I'm a bit drunk but what significance does 3 BTC have here?
If you mine solo and find a block doesn't it still pay 25 BTC plus transactions? If you mine in a pool then isn't what matters your rate of finding shares/hour? I can't think of any reason why 3 BTC is relevant to anything - it's 100 GH/S mining for Y*X time or 1 GH/S mining for 100*Y*X time : it's exixtence says nothing about what X or Y is.
when you mine in a pool, you set threshold payments so that after so much work, you will get paid X BTC (in this case, 3). This is so you don't get 100,000 deposits of 1 satoshi each to your account. If this 3 BTC payment repeats itself enough times, a hash rate can be calculated based on how long between payments. That's the idea anyway.
edit: please correct me if wrong here?