I am currently running 2 AI primes (non HD) over a 40B and have been considering adding 2 T5's once I get my Apex up and running. There is quite a bit of shadowing and disco effect and I think some T5's will help smooth that out. My tank is a mixed reef with about 50% being SPS of some kind (some sticks, lots of monti's, etc.) and I'm getting pretty decent growth with just the AI's but I also think running a pair of T5's during my day time hours will help with growth.