I have not seen it in this thread but could you give a brief river vs underworld breakdown? If you were willing to scrap them for underworlds i am dying to know what the contributing factors were.
Sure!
I'm a pretty new player who maxes out at a bit over 300', with 275' being a functional average for my drives. I've used Rivers in Gold line and Test Material, ranging from 163 to 170, and I've never had a River turn out of the box for me on a flat release: they've all be straight to fade, and will even fight out of an anny if I don't release them right (which, being a newbie, I am wont to do). I have to work to get them to turn over, at least until they beat in (which takes time in GL, and makes me paranoid about losing discs, which I am also wont to do).
The Underworld turns easily and predictably for me out of the box in either plastic. My 172 VIP holds its own in a crosswind, and can fly straight with a slight hyzer release or on lower power throws, or can hold a slow, gradual hyzer when released on a deeper hyzer angle. My 167 Tournament is awesome for slow, reliable turnovers, even on lower power throws or on low-flying tunnel shots.
I love how easy it is to turn these discs over (I throw exclusively RHBH, so perfecting turnovers is a focus of mine), and I love how the variation between the various plastics allows me to cover every line from stable to understable. The glide is at least comparable to the River's, and I've had a few throws with the Underworld that have far exceeded any other throws I've had (probably hitting 325' or so; a big deal for me). The VIP also handles the wind better than the Rivers I've thrown, although I haven't thrown a River in Opto at a comparable weight. So basically, out of the box, Underworlds can do everything Rivers can for me as well as some things that they can't, given their extra notch of understability.
There's a bunch of chatter
in here about these if you'd like some more info. Suffice it to say, I'm a huge fan.