SSJG3 Trunks ~ 50% Goku works fine imo, considering grade 3 Trunks was also above warm up Cell by a good margin. The Final Flash multiplier ought to be considerably superior to 2.2x considering Piccolo laughed at an attack with the same multiplier as the Saiyans Saga KMHMH. So I'd say Vegeta grade 3 FF would hurt Goku FPSSJ considerably, but I doubt it'd kill him.
100% Goku > 50% Goku > USSJ 2 Vegeta > Warm Up Goku
It most likely ends up in a similar situation to what happened to Cell. Vegeta is probably around 40-50% of Cell at the time and it looks like this is probably the case for Goku against USSJ 2 Vegeta.
Trunks seemed to be shitting bricks at Goku's power before he even realized whose power it was, so I'm more inclined to believe 50% Goku > Grade 3 Trunks than the other way around.
It's pretty clear what the scene shows. Everyone is completely dumbfounded by this new power. Except for Gohan of course. 50% Goku surpasses all. Plain and simple.