Well, when Goku left the Rosat, Vegeta asked him if he could beat Cell. After Goku witnessed Cell in his perfect form, he said he "probably" could not defeat him. So:
Perfect Cell >= Goku MSSJ
Trunks, surprised, said:
Trunks : "It's...that powerful?...I was afraid of that..."
This implies Trunks knew what Cell displayed earlier still was not close to his full power. So, in Trunks' mind:
Perfect Cell (estimated true power) >= Goku MSSJ (estimated true power) >>> Perfect Cell (warm up)
Even though, Goku's MSSJ (50%) power was able to impress everyone including Trunks, who even though that was his full power:
[+] Spoiler
Based on Trunks' reaction towards Goku's MSSJ (50%) power, I'd say this surpassed even Trunks' estimations of Goku's full power. So, we have:
Goku MSSJ (50%) > Perfect Cell (estimated true power) >= Goku MSSJ (estimated true power) >>> Perfect Cell (warm up);
Based on this, I find a little hard to have Trunks SSJG3 > or = to 50% Goku, unless you have SSJG3 Trunks way, way stronger than warm up Cell, what is not implied.