I'll chime in with the el cheapo alternative. The PureOne is, imo, about the best bang for the buck in the upper tier offerings. M1 is just too darn expensive for what extended benefits it provides. PureOne has proven effective for usage in the 10k range ..even over a year's time.
I would say that it would depend on how you put on your 6k. If it's a longer time-wise situation ..with semi-short trips ...lots of combustion byproducts ..then perhaps the finer filtration of the PureOne (or other premier filter) would be money well spent. OTOH, if you're zipping 6k out in a relatively short time span ..lots of long mileage at full warm up...then both the oil and the filter (of the level of PureOne, M1, etc.) are in excess of what you require for great service. From everything that I've gained here, I think most are well served (over served in some cases) with 6 month OCI's and adjusting the oil and filter to the demands of the mileage that occurs within that time span.