If you go synthetic Mobil 1 Synthetic gets my vote, it is considered one of the higher end group IV synthetic oils.
As for the synthetic oil being beneficial, I don't think the mileage matters a lot, and I do not think there would be a huge overall beneficial gain as far as engine life is concerned, as long as oil/oil filters are serviced regularly.
Now there may some benefits if you have cold winters where you live, the synthetic won't have as thick of a viscosity when cold, as a conventional oil would, but I believe once the oil warms up it will lubricate all the same, I get pretty cold winters here in VA, so I'll run only Mobil 1 Synthetic, or G-Oil.
If you are ok with spending a little more you could get the G-Oil, it is said to be a Group V synthetic motor oil.
To explain a bit better about synthetic oil groups I have to use the dreaded wikipedia, as I cannot explain it as well as it is explained there.
Wiki info below.
Motor oil - Wikipedia, the free encyclopedia
"""Synthetic oils are derived from either Group III, Group IV, or some Group V bases. Synthetics include classes of lubricants like synthetic esters as well as "others" like GTL (Methane Gas-to-Liquid) (Group V) and polyalpha-olefins (Group IV). Higher purity and therefore better property control theoretically means synthetic oil has better mechanical properties at extremes of high and low temperatures. The molecules are made large and "soft" enough to retain good viscosity at higher temperatures, yet branched molecular structures interfere with solidification and therefore allow flow at lower temperatures. Thus, although the viscosity still decreases as temperature increases, these synthetic motor oils have a higher viscosity index over the traditional petroleum base. Their specially designed properties allow a wider temperature range at higher and lower temperatures and often include a lower pour point. With their improved viscosity index, synthetic oils need lower levels of viscosity index improvers, which are the oil components most vulnerable to thermal and mechanical degradation as the oil ages, and thus they do not degrade as quickly as traditional motor oils. However, they still fill up with particulate matter, although the matter better suspends within the oil, and the oil filter still fills and clogs up over time. So, periodic oil and filter changes should still be done with synthetic oil; but some synthetic oil suppliers suggest that the intervals between oil changes can be longer, sometimes as long as 16,000-24,000 km (10,000–15,000 mi) primarily due to reduced degradation by oxidation."""
I have to disagree on the last part said there though, synthetic oil or not, I still feel changing it at the same scheduled intervals as non-synth oil is a must.