I want to do some high key "white limbo" shots on paper and I had a choice between white, white paper and a slightly warmer "polar white" and the Calumet guy talked me into the Polar White.

Do you think it matters that much? If I push the exposure up the paper will be true white anyway, so it seems the advantage of polar white is slightly warmer shadows and wrap areas.

If you want a background to be "removable" in PS let's say, you can use any color you like as long as you expose it properly.  I was practicing last night and had the white up and exposed it so it was black at the top fading down to gray at the bottom.  It really doesn't matter unless you want shadows.

personally im one of those guys that likes white to be super white.  i bleach the crap out of my white laundry...  so naturally id go with polar white if i were using a  paper background.  but if you want a REAL high key background then use a bigo soft box as the background and use the exposure setting for the front light.  thatll give ya a super duper white background

Once when I was printing type R (positive to positive) a client brought in several rolls from a shoot he had done for a company that made pom-poms for cheerleaders. The cheerleaders were wearing outfits that had white long sleeve tops and white boots and they were photographed on a white background. The film was Ektachrome 100 in 120 format and in EVERY shot the exposure was perfect, the background and the white clothing was white with detail and texture and you could see the outline of every boot and every top. I was pretty impressed, I set up a filter pack/exposure setting and printed his picks. Every print showed the same detail. Curious, I put a print on the densitometer and sure enough, the outfits were a warm white and the background was a cool white. When my client came in, I asked him about the shoot. He had used a Minolta color meter on the models and then lowered one of his THREE white backdrops! Pretty cool stuff.