I use a 2-3 inch strip of gaffer's tape, about 1.5 inch at the end of the film and then wrapping securely around the center spindle. If you want to be extra safe, the suggestion of wrapping tape all the way around to the emulsion side is good. However, I've found wrapping around the spindle to be sufficient (I don't use any motor drives), and it makes it easier to pull off when developing. That said, the center spindle on my bulk cassettes are solid without a slit, so perhaps more surface area to adhere to.
As far as Ultrafine Xtreme 400, I only have experience with it in 120 format. I've settled on using LegacyPro L110 (a HC-110 clone) at 1:31 (same as HC-110 Dilution B) for 5.5 minutes. Using that recipe, I get sufficient contrast for my tastes, which I can adjust in post-processing if needed. Contrast-wise I would rank Ultrafine Xtreme 400 < Ilford HP5+ < Kodak 400TX, at least in 120 format. Anyway, the proof is in the pudding, and I have an album of Ultrafine Xtreme 400 samples in my Flickr.