I used to think Pennzoil Ultra Platinum was the best of the best, but without PAO, Ester, and since it's on the thinner side of the 5W-30 grade (almost a 5W-20 by Kinetic Visosity @ 100C), I lost interest in it.
I also have doubt's on the anemic additiive package that Pennzoil oils have shown in virgin oil analysis here on BITOG.
Theoretically the GTL process yields an oil which flows better in the extreme cold and also resists oxidation better in extreme engine heat,
but it's unknown if these hot/cold temp advantages are only a negligable and tiny unmeasurable difference when compared with a regular group III full synthetic.
An interesting comparison would be Pennzoil's Ultra Platinum GTL based oil versus a low priced regular group III full synthetic like SuperTech. There might not be any noticable differences in extreme cold flow or extreme heat oxidation resistance between the 2.
Without any testing, my thinking is that all domestically produced group III and group III+ (GTL) oils are about the same in extreme cold / extreme heat flow/protection, and only differences will be seen if you compare with a Group IV (PAO) / Group V (AN + Ester) formulation.