Just curious why its all in the G? but as for split how far are you from retirement? If you're 37 and going for 57(assumption) you have at least 20 years left so i'd be very aggressive. You can weather some pretty big recessions over that time and still come out way ahead. I'd look at the L fund's for your year as a starting point then just wipe out the F and G contributions (e.g. ***made up numbers here*** L2040 is C 40%, S 20%, I 20%, G 10%, F 10% your investment pattern could be C 50% S 25% I 25%)
That's how my TSP looks and i'll leave it that way until i'm closer to retirement.
Also just personal opinion stay away from the F, when the fed eventually ups rates it'll take a beating