Gvr, Sorry for the slow response. As usual, a LOT going on....
This becomes a 'feel' thing. Accurate measurements and temperature, strangely enough, make an impressive difference. If you can catch your fingernail on a vertical stripe in the cylinder, expect oil usage. I won't build like that. I know the impulse is to 'cheat' and try another set of slight oversize piston rings, but we live by simple rules...'Do It Once and Do It Right.' 'Build It Like You're Gonna Buy It.' It may not be the cheap route, but the results are worth it. We do not like piston slap, as that is the reduction of the rings and cylinder walls life expectancy.
With the existing pistons at around 79.42, they are slightly worn and so is the block. I doubt the 79.51mm rings will work. Hone the block until squared up for Out of Round and taper. End gap 1st oversize rings to fit. Coat the pistons for .0015" clearance. I know I'm mixing metaphors, MM and Inches. 79.44mm is 3.1276". 79.51mm = 3.130". That is .0024" difference. That doesn't sound like much until your figure the engines we blueprint, we are using .0012" piston/ Cylinder wall clearance. Just the piston wear is double that. You probably need to hone larger than 79.51mm to clean up the cylinder walls in your situation. Although there are not pistons that are .010" (.25mm) oversize, we have the 1st oversize rings and coat the pistons to fit.
When we are using existing pistons, they are recoated with the graphite to fit with the bore. The slightly oversize rings CAN be a really cool trick, but the cylinder wear is a close tolerance when using the 79.51mm rings. Sometimes, we have to hone to an even larger size. We have done .010" (first oversize) rings and coated pistons to work.
The claim is that coating can be done to .020", but that seems excessive to me. If that is what is needed, I think using 2nd oversize pistons is the way to go. That is, if you can find them. We stick with Nural, Kolbenschmidt or Mahle, which seem to have been wiped out in the market for the time being.
The 'outsourced' pistons, I am no fan. If that's what it comes to, I'm retired. What Hans sells, I won't install. No way. Stuff from Saudi Arabia or the CRAP from China, like Engine Team; Nope... I'm not going to 'bottom feed' :/ The tolerances are not there. Piston weights vary too much. I don't trust the metallurgy. Other than that, they might be fine... LOL!