To me, 10 GI is really not that much to pedal. On a vintage 12 speed road bike it's basically the difference between odd or even gears. I run 46-16 on a 700 x 25 for the SS/FG, so that works out to 75.8 GI. On my 27" 12 speed, that's about 9th gear (73.9, 52-19), 7th gear is 63.38, 52-22. On a long incline in 110* F heat, of course that's a ball breaker, but flat land & after a few rides of pushing yourself and conditioning you'll be looking for more GI if you're after land speed records with it. I will add that on my 12 speed, 10th, 11th & 12th jump from 73.9 GI in 9th to 81, 87.8 & 100.3 for the final 3 speeds. Sometimes, I wish I had 52/42-12 with the road bike with a tail wind, it would give me 94.5 & 117 GI to work with too. That bike currently has 52-16 & 52-14 as the highest GI.

Where 10 GI makes a difference is how much more speed. With 7th gear on the road bike, I can get more rpm's and when I do that spinning, I feel more burn in the legs and get fatigued more easily. With 10 more GI, that matches a slower spin rate for me and while I can feel heavier legs, but there is no burning sensation from spinning faster.