my current headset set-up (temporary) is kind of odd. it's the sealed lowers from an aheadset with a 105 upper that's threaded to go with my fork. it's very difficult to get tight fore and aft without making it stiff to turn. i'm thinking there's no reason not to do this, is there? but also wondering if maybe there's something i don't know about that's causing it to give problems.

ummm. well... Death would be the reason I wouldn't do that...

I assume you kept the bearing race from your old fork and put it on the new fork, and left the bottom cup/sealed bearing installed on your frame... so you just changed the upper part of your headset right?
In theory it should work. maybe the top bearing is bad... is it loose ball?

well it seems to me that the crown race and lower head race function exactly the same in both threaded and threadless headsets. the upper assembly is the one that holds everything in place, be it the adjustable race and locknut (threaded) or the stem, starnut and top-cap (aheadset).

so can you actually explain specifically why this will cause Death?

Yeah, you should be fine.

I think maybe I'm misunderstanding what you are doing here... But either way: The reason I said death is that of all the things I might mess around with or hobble together on my bike.... The headset and cog (when brakeless) are two things I never get creative with. I know the top part of the headset is the business end and you'll probably be fine, I was just saying I wouldn't do something like that with such a critical area on my bike. Thats all. Don't freak - you'll probably fine, but I wouldn't do it permanently is all...

dude, as long as you maintain a certain speed you'll never have to turn your bars, so **** it, weld that thing solid!