Technically, a URL can be 2083 characters long but some say the real limit is 2000. I am not about to test this.
Okay. Not what you are looking for?
Remember that there is a lot of advice out there some of it very real, some silly as [redacted], and some culled completely from the dark smelly nether-regions (you know... New Jersey!).
The practical reality is that the URL should be short enough to be attractive and long enough to be descriptive. People will click on a longer link, but the psychology behind it seems to be that people will look at a link to see if they trust it. That being said, the URL should have the most important elements left most without too much suspicious gobblety-gook (technical term) following. It is a trust thing as much as a "Where the heck are you taking me?" thing.
It would be interesting to know that the URL to this question is 112 characters in length and truncated to 73 including any ellipsis (...) which I am including in my counts. That is a good length, but a shorter URL would be better. For example, questions/79166/ is 16 characters that is not needed.
Your largest size range of 80-100 seems okay to me.
The biggest things to remember is this:
- Dilute the ranking power of any given URL keyword
- May hurt usability and click-through rates
- May get cut off when people copy-and-paste
- May get cut off by social media applications
- Are a lot harder to remember
(Taken from: http://moz.com/blog/should-i-change-my-urls-for-seo)
As for search. Search engines do not care as long as the URL works. Really.
But I would like to address the Dilute the ranking power of any given URL keyword point made above. It is important that URLs,
description meta-tags, and
h1 tags should be tightly crafted to be succinct, properly keyword weighted, conversational, and catchy.
As for the 78 character length you mentioned, I took a truncated URL from the Google SERPs and counted 69 characters but I also saw one truncated at only 48 characters.
People do look at this of course. But I also suspect that they do what I do and hover the mouse over the SERP link. But still, this supports my theory that the most important elements be left most within the URL. Between the SERP link, the URL representation below, and the snippet (hopefully) taken from the description, all should all be supportive of each other and center on what a searcher is looking for- that is- search intent. In this case, it is about CTR.
I do no think it is important that you focus too much on URL length given what you have told us. But if you are able to shorten the URLs, then keep what I said in mind.