Is there a top limit to the speed I will be able to reach on a hybrid (trek 7,5fx) compared to exerting the same effort on a road bike? yes

Would a road bike help me go faster? yes

Or do I just need to be fitter and ride more to get faster on the bike I have? yes

As Eddie Mercxx says, should I ride upgrades, not buy upgrades? yes

Do I NEED a road bike to go faster? no

I think you need to define what you mean by going faster. Are you talking about increasing your average from 8 to 12 mph? Or 12 to 18 mph?

V.