More couterweights or closer conterweight ?

Closer weights are better. The moment of inertia (resistance to rotation) will be smaller.

The less weight you put on the system the better it is for the bearings to operate smoothly. On the other hand the harmonic response of the cantilevered weight is larger, for any given rod x-section, when the weight is further from the centre of action. If your counterweight bar is quite stiff that doesn't really change that much so you are better off moving the counterweight out than adding counterweights. Moment = Force x Length, so in each case the moment is the same. At high slewing speeds the centrifugal force would increase in the same way as far as the two options go (i.e., force=-angular speed^2 *Mass*Length), i.e., irrelevant which way you go.

Has anyone observed actual guiding or tracking error improvements for the "more" configuration relative to the "farther" configuration? For example what is the ROI of spending $$ to buy another counterweight? Does it really make any difference for a mid-range or better mount?

Many aspects of astro photography can be manipulated and adjusted simply based on personal or financial circumstances, environmental influences, or just individual style or flare.  This is not one of them.  This is not a topic for debate based on personal opinion and a survey result should reflect 100% support of the physical reality.  No offense to the OP and thank you to all the folks that have have issued posts reflecting the science on which the topic is based

You always want more weight to get the counter weights as close to the RA axis as possible.  As many have pointed out, that's important to reduce the rotational moment of inertia, which helps with motor torque and mount responsiveness during guiding.  Having a large rotational moment of inertia can cause motor stalls during slews because it makes the motor work harder to accelerate the scope.  However, the bigger reason to keep the weight "up high" is to raise the resonant mechanical frequency of the whole system, which reduces its sensitivity to vibration.  The added weight on the mount bearings is generally an insignificant effect.  Most common bearing assemblies used in small mounts can handle very high radial loads in the range of 100's and even 1,000's of pounds so adding another (say) 10 pounds is inconsequential.  The important thing is to maximize the stability of the mount--not to minimize its weight.  Here is a slide from one of my talks at NEAIC 2019 that should help clarify the point.  I'll have a bit more information on this topic at the next AIC meeting so I hope to see you there!

John

Well, in my case (EQ35M, unguided tracking with a 5kG Newt which is very close to the limit of the mount for astrophotography) there are exactly two ways to achieve balance:

1. 1 3kg counterweight at the very edge of the shaft. In fact it could use another 2-3mm of shaft if it were available but by fortunate coincidence my scope is always at the east when shooting so I don't mind that wee component of "telescope heavy".
2. 2x3kg countereights, one at the start of the shaft and one a few cm towards the middle

The first setup is very prone to vibrations. It takes 4-5 seconds for the system to stop vibating after a slew, or even if I so much as touch the scope e.g. to move a cable. But does perform very well if left alone. The main reason a sub must be dropped is because I walked in or out of the balcony, e.g. to grab a beer and my footsteps resonated with the whole system. I doubt it could handle guiding though and it absolutely sucks when there is the slightest wind. Which is why I tried the second setup. 

So the second setup is practically vibration free, but the mount is very obviously struggling to maintain tracking in RA. More than half of the subs have elongated stars. So I am using the "1 counterweight - farther" alternative and basically try to tiptoe withing 2m of the scope

I understand I am pushing it with the 5kg scope but based on what I am reading here the extra 3kg of counterweight shouldn't make such a dramatic difference, right? Perhaps I need to disassemble and see if there's anything physically wrong? The mount does seem to "dislike" it when the shaft is close to horizontal (e.g. telescope pointing at Zenith), even with lighter scopes. 

Cheers,
D.