All the proponents of the healing properties of Cayenne that I've ever read their byword is "the hotter the better" but when on a limited caloric intake protocol with no solids I would say it's more what each individual can tolerate. I've seen stuff in the 150 to 160 K stuff on the internet which makes my spinchter pucker just thinking about it ;+D
In the 6 years I've participated here pretty much the standard for many of us has become 1/4 tsp of 90K HU per drink. Some than can tolerate it have done more. Also in everything I've read 90K is the "minimum" to have any actual theraputic effect. So for some folks reading this FYI most regular commercial grocery store cayenne is pretty durn weak in the 20 to 30K HU range.