Heh heh heh, I dyno'd my 954 with snorkel and without snorkel. I had custom maps made for both setup. This was done on the same day and I gave the 954 time to cool down between runs. My findings were as follow;
With snorkel: 145.3 hp / 70.1 tq
Without snorkel: 145.3 hp / 70.4
Horsepower wise there real isn't that much difference, in the curve. It was pretty much the same.
The difference is in the delivery of the torque, so it's all going to be about where you like you torque to be.
Without snorkel beats with snorkel in torque delivery in the 4000-5500 and 10000-12300 rpms. The custom map had to make the lower rpms super rich, to keep the 954 from have a major bog.
With snorkel beats out without snorkel in the 5500-10000 rpms. I'm personally like the feel if the bike with snorkel, because I'm usually in the 5500-10000 rpms range at the track.
In the end each bike and rider is different, so take my little test with a grain of salt and do with it as you will.
Good luck and have fun!