Ohio code doesn't look to be too differently worded than Colorado or Texas, the two states that I've lived in. The code states that speed limits are set at the speed that 85% of the traffic is normally travelling. It does not state anywhere in that code, that the sign is a suggestion for the public.

In the year of living in Colorado, I have found that 10mph above the posted limit is the average everybody drives. Except I-70, if you are going anything less than 75mph (55mph posted) you WILL be passed and given rude signs.

On SantaFe drive, 45mph posted, I often see people pass at 65mph+ even with MANY speed traps.

And the HOV lane, don't dare get cought in it with only one person while the green lights are on, the fines are very generous.

I quoted a summary of Ohio speed limit determinations, not the ORC. It appears below. Note that the posted limit is not mentioned as a factor in what constitute's lawful speed. Also, I never said the posted limit was a suggestion, which implies optional regardless of conditions. I said it was a presumption that could be overcome in court. Likely? Hell no, but it's possible. This all matters less for a speeding ticket and more if someone is killed in an accident and one of the involved was going 5 mph over the speed limit, as liability attaches with negligence, which under your theory attaches at 5 mph over the posted limit. If a traffic study indicates that 85% of the traffic goes 45mph, and the posted limit is 35mph, than the lawful limit is 45mph, under the ORC. Of course, there's no study available 99% of the time to rebut the presumtive legality of the posted limit Here are sections of the code section.
§ 4511.21. Speed limits.

(A) No person shall operate a motor vehicle, trackless trolley, or streetcar at a speed greater or less than is reasonable or proper, having due regard to the traffic, surface, and width of the street or highway and any other conditions, and no person shall drive any motor vehicle, trackless trolley, or streetcar in and upon any street or highway at a greater speed than will permit the person to bring it to a stop within the assured clear distance ahead.
§ 4511.22. Slow speed.

(A) No person shall stop or operate a vehicle, trackless trolley, or street car at such a slow speed as to impede or block the normal and reasonable movement of traffic, except when stopping or reduced speed is necessary for safe operation or to comply with law.