I don't know anything about the 4600, but it looks like the normal HD shock. The 5100 shock was originally set up for lifted vehicles, and I had a set on my 05' Double Cab Tundra...and they were much heavier duty than the HD version. Are you looking to do both front and rear? If so, I would put Old Man Emu on the list for sure. For the rear I would recommend the OME 60002 and the 90004 for the front struts. They also make a front lift spring OME885, and for the rear I would look at the OME862 or OME865 (for more hight and load). If you do get the Bilsteins for the rear, I would recommend the FJ100 series shock and not the Sequoia shock as it's way too soft.
Read up more on the 5100 and it's not what I need. I just want to upgrade the suspension from stock. Just didn't know if the 4600 series is the same as the HD series. Bilstein's website doesn't even mention the 4600 series.