I agree with one of socute's suggestions: Jack off at least once within a few hours of getting together with your girlfriend. I am a big shooter like you, but generally the distances get less and less the more ejaculations I've had that day.
Not having been with an awful lot of different women, I'm not sure what most of them think of us guys who can hose down a room. It's something worth asking your GF about at some point, because if she likes the fireworks then you shouldn't go trying to tamp them down by rubbing one out beforehand. My wife really enjoys the "show" I can put on for her, but I had one previous GF who was extremely cum-phobic. Based on what others have said here, I tend to think most women (aside from the porn actresses who are paid to love semen) fall into the cum-averse group.