How much more energy, enough to make a difference ?
From the manufacturer's data, Hornady varmint express 55gr Vmax compared to Federal 40gr Vmax & calculated with a 200yd zero.
55gr, MV 3680 fps, ME 1654 ftlb
@ 300yds, V 2514 fps, E 772 ftlb
That's a loss of 882 ftlb which is 53% of its ME
Drop 4.9"
40gr, MV 4200 fps, ME 1567 ftlb
@ 300yds, V 2604 fps, E 602 ftlb
That's a loss of 965 ftlb which is 62% of its ME.
Drop 4.1"
So for an additional drop of just 0.8", the 55gr would be 170 ftlb up on the 40gr at 300 yds.
I tried a box of the Federal 40gr Vmax, they were very accurate and at the ranges I shoot foxes they were blowing them apart. I am currently using 55gr Blitzkings in my handloads and whilst they are just as accurate, they don't have the same explosive effect, but the fox is still dead before it hears the bang.
I'm using a Tikka T3X and the best factory I found for both accuracy and bag of soup effect were the Norma 50gr Vmax, but I believe they are now using their own ballistic tip bullets instead of Hornady's Vmax.