I had a pair of the 990 PRO's (i think) but sold them as i found i didnt use them much.
I've now got the 780's and they certainly seem to have much more bass to them. They're also much easier to drive and don't actually sound too bad without my headphone amp, whereas my old Beyers definately needed an amp
Are they uncomfortable to wear for a long time?
I guess it depends on your definition of long time, i don't think i've ever really worn them for more than a couple hours but i wouldnt say they were uncomfortable. Less so that my old Beyers but i think thats probably a difference between closed and open as the closed tend to be a little tighter.
I bought mine about 15 months ago and i have read reports now that the newer models have slightly softer ear pads