the 0W40 is a barely thin 40 with a viscosity of 14.0 cST.
the 5W40 is an barely thick 40 with a visc of 14.8 cST.
the mid 40wt cST viscosty is 14.4.
...although im currently adding VSOT, moly disulfide, and a quart of Redline 10W40 which gives it a viscosity of 15.5 cST and destroys the 0W rating heh.
the 5W40 has more boron and calcium, and less zddp and magnesium, and is thicker at 40C as well, which should lower my engine RPMS a bit under "cold" starting conditions. it is also my assumption that the 5W40 would have less polymeric VIIs, which is better for the summer since im gonna be putting my car through #@$%! muhahah!
if the UOA with the redline/vsot mix comes out ok i will probably add 1oz per sump quart VSOT and 1 qt of redline 5W30 to keep the viscosity stable (15.6 cST) while increasing ester content, moly and zddp a bit.