Which oil is thinner at start up?

So you are assuming the response curve is at least roughly linear?

Do you have anything that would support that assumption as valid? Seriously...I'm curious to know this!

 

Define problems then...
Sure you can run engine on anything you want, including soy oil but difference in the oil correlates to how long its going to take to degrade performance.This is a key thing to consider. Engine wear happens as it runs, depending on the quality of oil, it happens faster or slower but always occurs.
For somebody who purchased vehicle to drive for 30K miles and 3 years difference in quality between Walmart oil and lets say Rotella is not important. However for somebody who is planning to keep truck until wheels fell out it makes whole world of difference.

 

Well when the wheels fall off I suppose you got a problem...

Not everyone wants to turn car ownership into an obsessive hobby. I'm a little more careful than most but I won't keep it when the accumulation of nit-noying butt biters are so bad I can't stand it...that'll be around 150K miles, 13-14 years. In that time I could easily run Walmart blue bottle at 5K intervals with no problems...I fully expect the engine would run fine and be pulling great, just like yours.

No problems.

But I'll have replaced O2 sensors twice, cat once, alternator once (maybe), power steering pump once, clockspring once, and be so pissed that the frame has so much rust my wife won't let me park it in the drive anymore from the orange spots under it and oh, the A/C is blowing hot 'cause I just can't bring myself to blow a couple grand on a new compressor/condenser/evaporator replacement for such an old POS. Maybe not ALL those things but you get the picture...it ain't the motor.

And then, I could obsess over it on weekends coating the frame with black goop so it doesn't rust and replace all those annoying things as they go bad myself (so's I can pass the economical test of reason) and keep it another 10-15 years to the 300K point and drive it all beat up from parking lot dings, puffing blue smoke and putting a quart with every fill up using hot plugs to keep from misfiring and STILL be able to say with a straight face 'no problems'.

Or put the most exotic boutique oil in, changed at 3K intervals and NOT smoke blue but STILL be driving a POS with all those things I had to do with parking lot dings all over and then say...it's a POS.

Major problems.

I'm not driving a motor, I'm driving a truck and I'm thinking holistically by considering the whole package. The only reason I even use synthetic is so's I don't have to change oil so frequently 'cause the POS truck will be doing damn good to last 15 years and 180K or so before the economics point to buying new being cheaper than keeping it.

 

A lift and sliders eliminates 90% of parking lot dings.

 

Reactive armor the other 10% and 100% of the people who cause them.