I've got a few things to ad here...
4300K will be the brightest and most whitest bulb. 5000K will be slightly blue. You will start to wash out mild details on the road and lose a little bit of light output going this route, but it's not that bad. If you need that slight blue color, go 5000K and NOTHING above.
Regarding 35w and 55w ballasts -
The 55w ballasts will of course be brighter than the 35w counterpart. The increased wattage of the ballasts will generate a dramatic more amount of heat and this leads to their reliability. They will not last as long as a 35w ballast and this is the reason why all OEM manufacturers use 35w ballasts for OEM projector-equipped vehicles. The bulbs will also not last as long pushing that extra power!
Another issue with the 55w ballasts is how they pair to the particular projector being used. Just like how putting drop-in HID's in your factory halogen reflectors is a bad thing, so is putting a hugely powerful ballast/bulb combo in certain projectors. Certain projectors cannot handle the increased output and will start to lose the exceptional lighting characteristics that you are after, by doing a retrofit. Morimoto Mini's for example, paired with 55w ballasts, have even had their internal chrome finish burnt off. Yes, not a good thing, and TRS even recommends not pairing the two together!! Acura TL projectors and the LS430/460 projectors have been known to handle the 55w ballasts well. I'm honestly not too sure on the FX-R's and 55w ballasts but I've personally never recommended someone do it. Although the FX-R's are very solid so I would ASSUME you would be OK.
IMO stick with a 4300K bulb, but opt for the Philips 85122+ or the Osram product. These bulbs just have the quality and reputation to back up their slight increase in cost. I run the Philips and LOVE them. Pair them with a 35w ballast - Morimoto if your truck sees river/water crossings as they are weather sealed better than even the OEM Denso ballasts. Go with the Denso's if you crave that faster warm-up time and ultimate regular-driving reliability.