Adllewis, I'm in almost the exact same boat as you are, and in fact even in Seattle. My use of the Raptor isn't going to be the traditional desert runner either. Planning on getting a 20-22' travel trailer in a few years and putting a million miles on it...Route 66, Dalton Hwy, I-90 coast-to-coast, US-1 to the end in the Keys, etc. And plenty of Forest Service roads. I thought about a 250 myself, but don't want the trouble of a modern diesel, the Godzilla 7.3 just seems like overkill (and probably thirsty as f*ck), and I don't think the 250 would provide as much pure driving joy as the Raptor does. Plus, whenever I get to the next destination, I'll just unhook the trailer and I still have the Raptor to play with. I don't think a KR, or even Platinum 250 would also be as much fun, nor have the 'wow' factor of our Raptors. Plus, the bigger the truck, the more limit on where you can take it. And the stiffer suspension is going to compromise ride quality unless you're really loading it down. My plans, and what I'd suggest you do:
Upgrade the rear suspension...Deaver +2 or 3's, even the HD if you want more capacity/less rear end droop when you're loaded up for bear. You'll sacrifice a bit of road comfort, and maybe some off-road capability (or not if you get the upgraded bump stops, etc), but you'll be better able to handle the way you're equipping your rig. TO me this will be my biggest bang-for-the-buck improvement. When you get a trailer, consider a WD hitch. I rented a couple of trailers (17' R-pod and 21' conventional last year), and think with the soft standard springs that's a must. I may (or may not) forgo that when I put the Deavers on. I do NOT think I'll go for bigger rims or tires, I like that part of it just the way it is. I may go with some SPD turbo adapters, and already have a 170* thermostat (just not installed yet) to help keep temps down when towing. I do also already have a JLT catch-can, which collects enough oil to make me think it's worthwhile. Otherwise just lovingly maintain the EB engine to keep the internals/turbos clean and happy, change your rear diff fluid at 10K miles (and clean up the insides-you'll be shocked how much crud is suspended in the lube and adhering to the gears), tranny fluid at 20-30K (same reason) and then look forward to years of miles and fun.
Bottom line: Unless you're already nearing the max weight rating of your Raptor, and still have more gear to install (don't forget the weight if 1/2 tank of fuel, and any passengers), or truly need a bigger pickup bed, I don't think any 250 will be as satisfying to you. It sure wouldn't be to me.
Best to you whichever way you decide to go!
Thomas.