Anthony,
I'm running tanks with both IceCap and Universal ballasts, all IceCap retros.
Overdriving the lights gives you better PAR but consumes more power and runs the bulbs very hot so fans on the bulbs are a must, as mentioned earlier you will shorten the lifespan to 12 months or less.
Just to give you an idea, 4x54W on IceCap ballasts draw ~320 watts with PAR of 185 @ 18", same setup with Universal draw ~224 with PAR of 155 @ 18". PAR reading was with sensor directly under the lights. I have to look when I installed the lamps but they're probably close to a year old. Fans on the IceCap, no fans on the Universal. I have another IceCap setup on a 4x39W, no PAR but can get them, but the light draws the same 320 watts and I go through bulbs faster (within the year) on this setup as they over overdriven to almost double the rating.