Hi Horseman,
I also have heat issues in the summer. I've decided to use only my LEDs in summer and just one T5 on another table for mothers, seedlings, vegging.

My experience has been that a 4x48" T5 with my LEDs, in a grow cabinet still puts me into the danger zone (mid to high 80s). So, I'm not using it until I get past that major stretch in flower, probably for the last 4 weeks before harvest.

I refuse to A/C the grow area and a chiller won't work for me, so I'll probably end up a winter grower only. However, Rusty has a great thread on dealing with heat. Check it out.

Luck and keep cool,