#1
Anyone know of an article I can read up on to understand the differences better? Not finding much on google. Thanks
#2
Preamp distortion is a bit buzzy, crunchy, gritty, and growling. (metal for example, relies heavily on preamp gain). power tube saturation is creamy and smooth (classic rock).

You need to find the median between the two that best suits you based on what you're playing.

as for articles, im not sure and im too lazy

edit: found this, might help
http://guitarexpert.wordpress.com/2007/01/16/poweramp-and-preamp-saturation-the-key-to-srv/
Baron K2 SE 120
MILLS 4x12 Afterburner
Eventide TimeFactor Delays
ISP Pro Rack G Noise Suppressor
BKP Warpig pickups