This is the way I see it...150,000 miles and changing the oil an adverage of 5000 miles. Thats 30 oil changes...
Syn Oil............$4.50qt x 6 quarts = $27.00
K&N Oil filter....10.00ea.
Over the 150k miles, thats a total of $810.00 in oil, and $300.00 in oil filters for a grand total of $1110.00
Reg Oil............$1.20qt x 6 quarts = $7.20
Wix (LR) filter...$7.00ea
Over the 150k miles, thats $216.00 in oil, and 210.00 in filters, for a total of $426.00.
You can get by with a less expensive oil filter too, but I just used the LR filter as an example....
So, that's a $684.00 difference over 150,000 miles. Personally, I don't see the value. I'm sure the Syn oil reduces wear, and prolongs engine life some, but what's a few thousand miles worth? The motor is going to wear out anyway, and that $684.00+ can be put towards a new engine, IMO.