I actually went from using a 100% synthetic exclusively (from 15K to 30K, or so) to my blend of synthetic oils & dyno oils (typically a mix of 2 quarts synthetic and 4 quarts dino: ALWAYS the same brands from 30K to 75K, or so) to the last 50K using Chevron Supreme 10w30 (typically @ $0.59 per quart after rebate: SJ, SL & now SM)!!
Using 3K OCI's I've NEVER had any engine mechanical problems and my car runs as smoothly as it ever did once broken in. Normal PM items like timely timing belt replacements, fresh fuel filters, etc. all done regularly. I did have the water pump, the cam, oil pump & crankshaft seals all replaced @ approximately 120K, but that was normal service as far as I was concerned, considering it is a 13 year-old Subaru SVX.
The newest conventional oils are just amazing IMHO. They perform so well that anyone who can SAFELY use the "normal" weights (say weights from 5W-20 to 20W-50) by using 3K OCI's & a quality filter is pretty much throwing money away to buy oil that costs up to $6+ per quart. A SuperTech filter and 6 quarts of Chevron Surpreme costs me a little over $5.
Except if you REALLY want to use a 15w40 HDEO: THEN it costs a $ to $1.50 per quart!
Cheers!
p.s. I do have a weekly curbside recycling pick-up of used oil as long as it is in clear plastic milk jugs.