I think the OLM is pretty accurate vs a static mileage, but I much prefer a structured MX schedule around mileage. Every other part of the car (tires, tranny, diffs, coolant, etc) is centered around mileage, so I prefer my OCI to be mileage base as well.
My 5.3 LS1 goes about 4500 on the OLM, but my 2.4 Ecotec goes about 8500. I usually use about 3750 on the LS1 and 7500 on the Ecotec. Easier for me to keep track of. I certainly don't discredit the OLM, and if it signals for a change before my static numbers, then I go by that.