I will let you do the research yourself. Take a look at Sanjay's Lighting site
. He tested bulbs with different electronic ballasts and then you can see for yourself, in hard #'s, how much difference there is between them. There is a bigger difference in the CCT (color) between the ballasts than there is in PPFD (PAR) output. You probably saw that difference. Looks like the IceCap burns the bulb whiter in your case, but that doesn't mean it's putting out any more PAR.
Here's a few examples.
Coralvue 250W 12k: IceCap ballast - 56 PPFD, ReefFanatic - 52 PPFD
Phoenix HexArc 250W 14k: IceCap ballast - 73 PPFD, Blueline - 74 PPFD, ReefFanatic - 76 PPFD, EVC - 79 PPFD
XM 250W 15k: IceCap ballast - 47 PPFD, Blueline - 41 PPFD, ReefFanatic - 53 PPFD, EVC - 50 PPFD