Well, my interpretation is that yes, it would still be metered, the limitation being the 5%. If you consider that no matter what, usage must be regulated by some factor.
reg·u·late
tr.v. To control or direct according to rule, principle, or law.
also:
1. To adjust by rule, method, or established mode; to direct by rule or restriction.
I believe that you are adjusting (allowing more transfer or not), based on the 5% rule/restriction.
I don't feel the terms unmetered or unlimited relate to web hosting very well. A new word is needed to describe what you are talking about (which I fully understand). I'll look for it and see if I can come up with something.
'Resource Based Limit' is too long (maybe 'RBL' ???), and doesn't sound extremely attractive I'll admit, though it is the most accurate phrase I can think of off the top of my head. '100 Gigs or 5% CPU' ???