That's 2% less total weight at the expense of about 7 mins flight time. Small gain for huge loss.
 Just to be clear that's a 2% drop in wieght for a 33% decrease in flight time going from 75% to 50% fuel.
While the reduced fuel 
might make you slighly more nimble the decrease in flight time would severely impact your stats:
Lets say you are averaging 3 K/D and 2 K/S at 100% fuel load and decide to decrease fuel to 50%.  If the numbers above translated directly (which is doubtful) you'r K/D would go up to 3.1 (4% gain) while your K/S would decrease to 1.0 (50% loss).  I can guarantee that you would move 
down in the pilot rankings.
I want enough fuel onboard to land multi-kill sorties.  Even at 100% internal I can't tell you how often I have to rtb for fuel when I'd rather stay out fighting and I've never felt disadvantaged with the extra fuel.
I won't drop the sipper on the Spits until it's dry.  Even in a fight.  In the F6F if I get into a fight before I'm able to drop ord I'll drop the bombs and fight with the rockets still in the rails.  Once you're used to it it's really not a hinderence.  It's no different than any other non-similar aircraft match-ups.  The guy with superior knowlede of ACM's is going to win regardless of how his plane is loaded.