datil, welcome to the forum!
There is a persistent myth that burning media at the slowest speed makes it more compatible with consoles and/or gives the best burn quality.
This myth is in general not true, and for modern high-speed media on high-speed burners can actually in some cases lead directly to completely unreadable discs!
Your Plextor PX-716 should be able to burn these DVDs at all supported burning speeds with good quality. I suggest you try burning at 6x which often gives the best quality on Plextor drives for such media, but the compatibility with your console will probably be the same whether you burn at 4x, 6x, 8x or 12x on that burner with that media.
No software can force a drive to burn media at a speed that the drive isn't capable of, and your high-speed Plextor burner cannot burn that media slower than 4x.
Try it out and let us know how it works.