Along with making sure you have a fan to cool the bulbs a bit, You need to determine the focal point within the parabola of the reflectors and place the center of the bulb there (or as close to it as you can get) to achieve maximum results. All you need to determine this is the width and height of the reflectors. If they are not a perfect curve, don't worry, you can assume a perfect parabola and still achieve similar results.
My Tek II reflectors (not perfect parabolas) which are 2 1/4 " wide and tall, I believe had a focal length of 1.75" which meant I had to raise up the reflectors a 1/2" to get the focal point near the center of the bulb. My end caps had raised the bulb up too far. You can find the formula for determining this on Wikipedia. I can't remember off the top of my head.
Just upgraded from PCs to T5,s whoa what a difference. Added my first SPS a couple weeks ago and so far everything looks good. Tortusa even kept it's tri color. :-)