Yeah I thought it might be a TT fan, I bought one many years ago, they just are not fit for the job mate.
I would look for a ruck/can or RVK , you should be able to get one new for around £65 or pick up a second hand one for about £20-30.
You shouldn't even need a 6" but since your already having issues with heat better to go big and play safe.
Pick yourself up a 6" filter which matches the CFM or m3ph. It can't be less cfm than the fan.
@jondamon runs 400w hps, perhaps he can chime in on what his specific set up is and add his thoughts.
Like I say, it shouldn't be difficult to maintain good environment.
I know you started this thread with LED in mind and you can still go that route if you want, but its gona cost far more to do it right and I see the easier and cheaper option is to sort out your ventilation first. Even if you went with LED you would probably end up needing to sort out your ventilation anyway.