What
@gunsnjeeps and other said. Main question is are you running a bolt or auto. Military or commercial brass etc... There are variables here to consider. You can load a bolt hotter than an auto and I would hesitate to recommend running at the top of the load range for an auto.
The 10% of max is a standard rule of thumb, but if you're dealing with a fast burning powder, you'd probably be better served starting between minimum to 1/2 max charge weight. I usually try to find same weight bullet, same shape and same powder for stuff not listed if it's a commercial round. If it's a handloader special, and not the latest greatest, the Pet Loads book or P.O. Ackley books can be of assistance. If that doesn't work find similar powder nearest to the burn rate of yours and shoot for the middle ground. There are a couple of applications like Dan Newberry's OCW and Quickload which can help make intelligent decisions as well.
One thing to note, if it's not a new powder, bullet, cartridge, and your google foo doesn't yield much there's probably a reason people aren't using that combo. Doesn't mean it won't work, just means the accuracy potential left something to be desired or it was a finicky load.
In this case, 4064 and a 168 HPBT is an old school load. Start with 42gr 4064, Fed GMM / Std 210, CCI or Win primers and go from there if necessary. This is an old military load that has worked for years. Typically you'll find a node between there and 43.5. 2.800" is a standard load length and most of the book lengths are based on magazine length. If you want other options, H4895, I4895 and Varget. Accurateshooter is a good source of info.
One other thing, you'll notice a lot of the books today say version 10 vs version 7 they dial back the loads a couple of grains. Hence the reason I usually start in the low middle and work up from there.