Also found a "Grolux" HPS which looks good.

I'd be tempted to stick with a regular HPS bulb for your purposes. You already have natural light providing a better spectrum than any bulb. Plus you are aiming for flowering and fruiting rather than maximum vegetative growth, I think, so HPS should be perfect.

I do have natural light, but in the dreary dead of winter I'll actually be getting more light from the HPS than from the sun.

But, yes, I do want flowering/fruiting.

Go w/ the ceramic metal halide by philips. You won't be disappointed!

That light looks promising, but doesn't come in high enough wattage to be beneficial (it would only provide an additional 300 foot-candles or so unless I had 3 or 4 of them).

Are there plans to release a 1000 watt version?

Not to my knowledge.