I understand that balancing a telephoto lens is important, and that the balance point changes as you add extension tubes, flash etc, so I am thinking perhaps the Wimberley P20 would be better as it looks longer and should provide more scope for balance.
The foot on both those lenses is relatively small, so the plate you've linked to will work for both lenses. If you later move up to the 500mm f/4L, you'll need a longer plate with two screws, but that lens is way longer and heavier than either of your two.
I personally use only RRS lens plates. they are solid and hold well in tripod heads. I use a Mongoose 3,5 B and my %00 f4 with a RRS plate without any problems
I have a Kirk bh-3 ballhead and a newly acquired Mongoose 2.3 gimbal. I use the Kirk LP-5 which was specifically designed for my 400mm f.5.6 lens. Kirk has a number of plates specifically designed for lenses and cameras. I use the ones that are designed for my gear.