Two quite different things lead to that charge. One is conduct: driving in wilful or wanton disregard for the safety of others, which is a judgement made by an officer and then by a court, and which has no speed attached to it at all. The other is arithmetic: in some states a stated speed above the limit is reckless driving by definition, whatever the driving looked like.
The second is the one drivers cross without knowing. The table further down this page lists every state whose statute names a stated speed on a first offence, with the offence it becomes and the section that says so, checked state by state against the statute rather than assembled from secondary sources.