if cost is no object Amsoil Signiture series. a close sseocnd would be Pennziol Ultra platinum. Even the Amsoil commercial....aahheemmm. reviewer... on youtube said if you cant get Amsoil then use PUP.
It to is relatively inexpensive at walamart now at $20.xx /5 qt jug.
really i would make a first run with regular synthetic and see what the results are. if its obviously thinned out at the end of an oci, then switch to something else, if not the do a single UOI to see if the visual analysis matches a lab test.
I tow my boat with a regular 2007 4.0v6 toyota tacoma and run whatever is on sale. everything from M1,PP, PUP, RGT, QSUD, PYB, ST. Magnetec, valvoline
not much difference between any of them after a 5k oci. I get oil so cheap (anywhere from getting paid -$2/jug to $12/5qt jug (sales/clearance/rebates) i dont bother with a 10k oci.