For the most part, I'd say portability in terms of length and weight is relative. Heavy to you might not be heavy to me, or vice versa. The weight of the gear you need to support is also a factor to consider.
One non-subjective limit is length of the tripod if you will travel by air. If I remove the head from my 4-section tripod, it will fit inside my Storm im2500 carry-on hard case - a 3-section or taller 4-section would not. OTOH, while my tripod does fine with a 1-series body and big white zoom (70-200/2.8, 100-400, etc.), it is not sturdy enough to support a supertele lens. When I eventually pick one of those up, I will need a new tripod as well, most likely a Gitzo 3-series or a RRS.