This is old, from 2000 but I wanted to post it regardless.
Simon G, and for the readers information, I will print the test data done for Lubrication Engineers on 5w30 oils. Two tests were done, the ASTM D-2670 Falex pin and vee block wear test with results of pass or fail. If the oil passed then the lower number of teeth shows the lower wear. Each tooth correlates to .0000556 of wear on the pin and vee blocks. The other test was an ASTM D-4742 TFOUT oxidation test. In the TFOUT test the higher number shows the ability to resist oxidation better.
Oils Tested --- P/F--- Teeth---TFOUT
Castrol GTX Fail N/A 121
Havoline Formula 3 Pass 14 193
Honda Pass 14 323
Lubrication Engineers Pass 6 481
Mobil Pass 16 218
Mobil-1 Pass 12 509
Mopar Pass 19 237
Motorcraft Fail N/A 207
GM Goodwrench Pass 16 221
Pennzoil Fail N/A 231
Quaker State Pass 11 157
Total Quartz 5000 Pass 17 219
Toyota Pass 14 222
Phillips 66 tropartic Pass 17 153
Valvoline All Climate Pass 17 247
Valvoline Durablend Fail N/A 166
Western Auto Fail N/A 190
As you can see by looking at the Mobil oils, in this case the Mobil-1 synthetic had less wear and much better oxidation than the Mobil petro oil. But that is not the case with the Valvoline all climate vs the Valvoline Durablend. The Valvoline all climate petro oil had less wear and more oxidation resistance than the Valvoline durablend synthetic blend.
The difference in synthetic and petro depends on the manufacturer. Valvoline's synthetic blend is not as good as the Valvoline petro. Valvoline petro is only as good as the Mobil petro oil. So in this case the synthetic blend of Valvolines' shows that going Valvolines' synthetic blend is a wase of money. However if you look at the numbers of Mobil-1 or Lubrication Engineers It would be worth the money. It's not weather a synthetic beats a petro or a petro beats a synthetic it's what kind of money and technology the manufacturer wants to put into their product. It's obvious in the chart above that Mobil-1 and Lubrication Engineers spare no money or technology in producing the best oil that is possible.
The best oil will be the one that has the lowest wear combined with the highest oxidation resistance number. The Lubrication Engineers SPB (synthetic petro blend) oil had 1/2 the wear than the others petro or synthetic and was close to the oxidation resistance of the Mobil-1 synthetic. I would rather have the lower wear and slightly less oxidation resistance, than higher wear and slightly better oxidation resistance. These tests prove that the best oil is the Lubrication Engineers SPB for the F 150 application.
You can also see that the average oil for oxidation resistance is about 200. The poor oils are less than 170, and the best oils for oxidation resistance approach 500.
You can see that the average oil for wear is in the 11 to 19 range with the poor oils failing the test, and the best oil for wear is at 6.
Sorry these are the only 5w30’s we have had tested to date.
I hope this information helps