I just checked out Escobal's book, Aquatic Systems Engineering. It's a great book, pretty indepth, but here's what I gather would be "best" for your setup listed...
Going with a 300g setup, to sterilize 99.99% of the total system water twice a day, you would need a flow rate of about 230gph through a sterilizer.
Going by a 64watt, 3inch diameter sterilizer (the largest the book describes), you would get a dose rate enough to kill about 90% of the listed organisms, including all bacteria and yeasts, but excluding parameium, nematode eggs, and about 50% of the mold spores.
Apparently, a 3" model is optimal, an inch larger or smaller reduces the dose about 33% because of the farther the light has to travel.
It recommends running your UV as little time as possible within the guidelines of flowrate and required dose rate, but you would need either a very powerful unit or mulitple ones to burn less than 24hour a day. This recommendation is for bulb life.
It also does not recommend using a quartz sleeve. It reduces the bulb effectiveness by 26%. He says the bulb will run cooler without one anyway, and the sleeve will need cleaning before the bulb needs to be replaced anyway, so unless you get one of those cool internal squeegee deals, it doesn't make the maintenance any easier.
Sorry about the rambling...
Hope this helps a little!