You will notice a great deal of heat with the HPS as compared to your t-5's. I have 2 150 watt hps lights and 2 2' t-5's in my flower chamber right now.

To give you an idea of how the heat rose for me:
originally i had just the t-5's and the one hps. Temps in my 2x3 flower chamber were some where around 80-82 degrees. when i put the other hps in there the temps soared to 95- 102 degrees!

I would say it is worth it to use the HPS in conjunction with the t-5's. Not only would you increase the lumens inside but with the t-5 & HPS it would be alot easier to control temps.

Plus mary-jane just seems to love HPS lights!

hope that helps.