i've used the UTC threads some.....pretty nice stuff.........flattens great.......seems a bit slippery though.......probably "splits" great for makin' loops.....never tried it.......
i can't stand Uni-thread.........it doesn't flatten easily at all..........you can do it, but it's a pain............the 8/0 is actually good for a lot of smaller Trout flies (better to use Bennechi), but i simply don't tye those much anymore............i have THOUSANDS of flies for Trout fishing (and everything else) so i really never need to tye another Trout fly ever.............although i do because i love tying them.......(specially wets).......but it's usually for Misa's team mates and Misa, or if somebody ask for somethin' particular and i'm gettin' paid.
Again, Uni always seems to be "dry" (if that makes any sense).....i just don't like the texture of it.............and it's always got to much twist in it...........and it breaks way to easily, for me anyway.....i think it's gets "old" to quick.....or something.....couldn't care less if i ever use it again, for anything.
My staple thread is Danville 6/0..........almost always primrose or white.......the primrose creates less glare.........but both are so easy to see when flattening. It flattens great and is very strong, and easy to control.
i also like Bennechi(sp?) 12/0 very much (amazingly strong for being such a small denier), and the Griffith's 14/0 and Sheer 14/0.......the Guedbroad(sp?) was nice stuff but it's history.....
but picture this...............the same fly (more or less), on a blind eye hook, bout a size 3/0, w/ a tiny bit of K.F. in the tail.....the grizzly palmered ("through") a seriously dubbed and picked out thorax and providing the first couple turns of collar.....same rear body.....same front hackle.....with drouping JC nails. 
