The Toyota oil TSB's changed their recommendation to ILSAC GF-4 oil (circa 2006) and also say it is ok to use ILSAC GF-4 5W-20 in some engines. Search out and check the oil TSB's to see if your engine is included.
Hm... Amsoil ASM 0W-20 with an EaO23 filter to bump up oil capacity to 5 quarts run for 15,000 km could be interesting. Never been into extended drains, but if I get a UOA done on the current oil, use a good filter, and the ASM which seems to bottom out grade wise at 8.5 cSt would be really good, and the logic in my mind behind it that the total cost of running GTX 5W-20 or Pennzoil 5W-30, and a Wix filter for 5000 km amounts to the same as running ASM 0W-20 with the EaO23 filter. The longest OCI this car has ever seen was 6200 miles (unintentionally) with Pennzoil 5W-30 and a Wix filter, and that oil came out pretty tired but I didn't think at the time to get it analysed.
Might be an interesting compare and contrast type thing...I just don't put on enough miles to get everything done with this car I want to try out. I want to UOA my current fill of Mobil 1 at 5000 km, I want to run a cycle of AutoRX to clean out the engine, and I want to try 5W-20 to see if I get a mileage improvement or see no wear change, then if that works out I want to try 0W-20 on an extended drain to see if I get any benefit out of it. But of course, by then, what I have spent on UOAs will probably claw back any savings I ever make.
I have been BITOG'd.
So what if your UOA costs more than just changing out regular oil much sooner...that's the price of Knowledge. And, with that Knowledge, you can recoup your money on future extended drains. I now at least DOUBLE my drains over the Manufacturer's recommendations because of the Knowledge I've gained from UOA's.
I really only want to extend drains enough to recover the cost difference per oil change between dinosaur juice and synthetic, the fuel economy improvement is the gravy.
The M1 in right now is in purely for a performance reason in cold weather, and it was the most readily available product to fill that need.
Oil and filter going from $19 to $63 means going from 3000 miles to 10000 miles to come out equal for costs of materials to break even to not lose the fuel economy gains to lube/filter costs.
The UOA thing bumps the hurdle higher for the fuel economy gain to ever really show a return. Cost effective gains are what I am seeking here, it's all an opportunity cost I guess.