Advice needed from the Ph-Meter savvy brewers out there

I would think the 7.0 and 4 would be fine, as we are dealing with data in that range.

7.0 balances the circuit, 4 sets the gain. I go back to 7 to see and correct for interactions, then check the 4 again. If I check at 10 it shows how linear it is over a wide range, but that is often a little off.

 

+1. Always wise to go back and check the measured values of your calibration buffers!

To the OP: 6.86 and 9.18? I've never seen a pH standard solution with such seemingly random values. You can find buffers from pH 1.00 through 14.00 (usually +/- 0.02 at RT) in 500 mL bottles from a number of sources online for anywhere from ~ $15 to $70 (if you need a CoA - which you don't).

Anyway, as long as your meter lets you choose the number of buffers AND lets you enter the pH value for each calibration point? A 2 point curve from 4 - 7 is perfectly fine (assuming you're using it to check the pH of your mash). If you're going to use it to check and adjust your strike water pH? You might want to use the third point. My well water pH is a lot higher than 7.