wow, how the hell did I miss this thread? LOL.
"The smallest but the brightest", never find it, heh heh. I've never seen the 1700's myself but I have seen pics and they look pretty good. I'd recommend the 1400's for ya. Rick and Bill Kemp both use them as backup lights and I'm hoping to mount some up soon as well. They are really small and the light they produce is amazing. The fog's have a great spread on them. I have some pics of them mounted on Ricks bumper somewhere, I'll look for it and try to post it.
The 80 XT's or the 80 Rally's are going to be the brightest you can get from PIAA, but they are also the biggest. The exception is the HID system they offer, which are quite size efficient, run a low wattage, but also cost a whole hell of a lot. They are rated at a little less then twice the candlepower of hte 80 XT's, as I recall the HID's produce 550,000 candlepower per bulb, while the 80 XT's produce 385,000.
The 1500's will be one of your best fog lights, but they aren't super small. And they have unfortunately enough discontinued the clear fog version.