I think the safest bet (and a very high quality one at that) is Mike's tape from ATR Services. It's in his best interest to have a really good tape stock to use on his pricey-but-worth-it refurbed machines, so he'll continue to make it past the point that AGFA/BASF/EMTEC/Whatevertheyaretoday will cease to see the economic sense in continuing to make tape stock for an ever-shrinking audience.
Try it. All comments seem to be positive. Midway between 456 and 499 in setup.
Oh, and +1 on the 250/996, too.