Funny you mention that... My lifters quit ticking after i changed the oil last week. I generally go by the DIC, or 5000 miles, whichever is sooner. When I changed it last, I had gone about 5200 miles and had 56% life left according to the DIC. I lose a quart every 3500-4000 miles and I do check it regularly and keep it full.
I guess I should start changing it sooner. And im also at just about 225k.