I use the Korss 400(L) all the time. In fact, I basically stopped using SIB weapons when I was able to pick up a Korss. There are very few instances where I switch weapons....
If I cannot loot a Korss, or get one on auc at a decent MV, then I get a Breer P5 (L). It is a bit slower in the re-fire (50 shots/second, vs. 57 shots/sec) but it gets the job done, and does a bit more DPS.
On occassion, I will get a higher lvl pistol, but usually if I am going on a big soc hunt with big mobs.
Personally, I do not think the increased DPS for the HL8, 11 & 12 is worth the markup. On the plus side, once you hit lvl 39 laser pistoleer/ranged laser, the HL 14 (L) is a great pistol, and market value is falling, since the frescoquoda seems to drop them a lot.
My advice, keep plugging away with the korss/P5, unless you absolutely need a bigger pistol with more DPS.