upgrading from 4 bulb to 6 bulb T5 fixture - make a difference?

ATI makes SLR T5 setups, also Ice Cap came out with a fixture using the same reflectors as in it's retro kits.

 

It will help but I would look into the quality of your current bulbs and reflectors as well before adding more electricity draw to your system. Good bulbs and reflectors can make a huge difference and use no more electricity.

Sunlight Supply makes their Tek line of fixtures with SLRs.

As for clams different clams need different amounts of light, you might also consider what their natural environment is when placing them as well, some live on the substrate in the wild, some live on the rocks.
http://www.wetwebmedia.com/ca/volume_4/V4I3/Tridacna/artGotTridacna.htm

 

Well our acros don't really grow. But they aren't dying. So it's like they're in their never-never land of growth. We have an ATI Blue Plus, UVL Super Actinic, A UVL 10000K AquaSun, and a Giesemann "Midday" bulb in there right now, but all of those are ready to be replaced. They're in a Sundial T5 fixture and we're thinking about going to a Nova Extreme Pro fixture. Or another 6 bulb fixture. The Nova is what we're leaning towards.

 

I have a nova myself. I've been satisfied with it so far. Only downside for the product is their warranty. If you use anything other than their bulbs in the fixture i'm fairly certain it voids the warranty. So I'm using their bulbs until my warranty is done and then putting some "higher end" bulbs in afterward.

 

Yeah we'll probably use their bulbs until they're ready to be replaced after about 6 months. I'm sure we'll find out if the fixture has any problems during the first 6 months, so I won't feel bad stuffing some better bulbs in their later on Plus going with the lower quality bulbs that come with the fixture will help light acclimate everything better.

 

K+ took the words right out of my mouth. This is the way to go. I get my lights from www.reefgeek.com I can't find these lights in the stores. All they seem to have is coralife and that is probably ok but if you want a bluer look than get the aforementioned lights. Put a Blue+ on the front and rear and middle. The others go where you like them. I use 8 deep T5 fixtures and my bulb setup from front to rear is as follows:
ATI blue plus
GE 6500K
UVL 75/25 (14K)
ATI Blue plus
UVL Aquasun (pink 10K)
ATI Blue plus
ATI Aquablue (12K)
ATI blue plus
This was recommended by an expert in T5 lighting. This is what my tank looks like. I would recommend that any SPS corals be high up on the rocks. Also my tank is 29" high and my bulbs are 6" above the water. These bulbs are over a year old and are still running well.