Good morning:
I've run the original 7.1 Pro install, 7.6.1 and 8.1 on my 840av (24 megs of RAM). They all run fine, and they're perhaps all worth looking at in terms of the machine's history.
The only version I've never really bothered with is 7.5.x. 7.6.1 offers significant technical and minor quality of life updates that, in my experience make it worth running over any version of 7.5. It's not meaningfully heavier even on '030s and you can strip all the same stuff out of it as in 7.5 if you need it to be significantly lighter and faster. (I'm aware that I'm in the minority on this one.)
7.1 is likely what an Actual Graphics Professional who wanted to maintain full performance would have run. By the time 7.5 and 7.6.1 launched, you could get PPC Macs and most software was PPC native.
8.0 (really, 8.1 so you get HFS+ and some other tech benefits) runs fine on these as well, but that's so far beyond this machine's prime that a lot of software was starting to become PPC-only, up to and including "basic" things like Office 98.
So, some of this depends on what phase of the machine's life you want to experience.
You do not need to match the actual software to the OS version you run, for example you can run 7.1 era software on 7.6.1 or even 8.1, just to get the benefit of the updated OS.
A lot of why people ever ran 8.1 on these in the wild was stuff like cascading a machine around to different use cases or a machine having been sold and then bought and used later on. Though, "running 8.1 on an 840av in 1998" and "running 8.1 on an 840av in 2003" are also fairly different, and a lot of this depends on, well, the use case.
A way I've been thinking about framing things is... if you're going with simulating some previous experience, what point in the machine's life are you simulating? (That's a big if because sometimes you just want to do clarisworks, hypercard, and oregon trail tourism and any OS that runs on an 840av will do all of that extremely well.)
I've run the original 7.1 Pro install, 7.6.1 and 8.1 on my 840av (24 megs of RAM). They all run fine, and they're perhaps all worth looking at in terms of the machine's history.
The only version I've never really bothered with is 7.5.x. 7.6.1 offers significant technical and minor quality of life updates that, in my experience make it worth running over any version of 7.5. It's not meaningfully heavier even on '030s and you can strip all the same stuff out of it as in 7.5 if you need it to be significantly lighter and faster. (I'm aware that I'm in the minority on this one.)
7.1 is likely what an Actual Graphics Professional who wanted to maintain full performance would have run. By the time 7.5 and 7.6.1 launched, you could get PPC Macs and most software was PPC native.
8.0 (really, 8.1 so you get HFS+ and some other tech benefits) runs fine on these as well, but that's so far beyond this machine's prime that a lot of software was starting to become PPC-only, up to and including "basic" things like Office 98.
So, some of this depends on what phase of the machine's life you want to experience.
You do not need to match the actual software to the OS version you run, for example you can run 7.1 era software on 7.6.1 or even 8.1, just to get the benefit of the updated OS.
A lot of why people ever ran 8.1 on these in the wild was stuff like cascading a machine around to different use cases or a machine having been sold and then bought and used later on. Though, "running 8.1 on an 840av in 1998" and "running 8.1 on an 840av in 2003" are also fairly different, and a lot of this depends on, well, the use case.
A way I've been thinking about framing things is... if you're going with simulating some previous experience, what point in the machine's life are you simulating? (That's a big if because sometimes you just want to do clarisworks, hypercard, and oregon trail tourism and any OS that runs on an 840av will do all of that extremely well.)