If you feel metal particles or that sandy feeling, it means that your filter does not filter as much as say bosch, baldwin or fleetguard.
I've tried using Vic oil filters and even after 3,000kms the sandy feeling is obvious already. Guys here who have tried bosch, baldwins and fleetguards does not experience this even fter 8,000kms (i've tried bosch for 5,000kms and the oil does not feel sandy at all).
For the lifespan of the oil or effective oils out there designed for extended drain interval, back read ka and you learn that even mineral oils like delo gold ultra, shell rimula x, mobil delvac mx can be extended to 10,000kms or more depending upon the filter. I admit tht a used oil analysis is best to determine maxmimun usage of oil but HD diesel oils are deisgned for fleet service and can be used up to 30,000kms or more without breaking the oil yet. Again filtration is the key.
So worry about your kind of filter and I assure you that you don't have to worry about extending
CH-4/CI-4-CI-4+ API rated oils up to 10,000kms. A few pages back is a picture of sir zix888's
baldwin bd28 with Mobil1 TDT 5w40 at 12,000kms. You can clearly see that the filter is not clogged yet and oil is still not jelly like in nature. It is still very fluid.
