I have 5 Hornets... one 17 K Hornet, three 22 K Hornets, & one regular 22 Hornet ( since I own the reamer, I may make them all K Hornets )
the K Hornet eliminates the long taper, the "K" case headspaces on the sharp shoulder rather than the rim, this is supposed to help with both accuracy, & case life... they don't seem to grow as easily or as much, when sitting on the shoulder, rather than the rim...
one may notice only marginal velocity gains... maybe a couple 100 fps, but I'd suspect that's related to the case being unable to take any more pressure... or noticeably people are trying to stuff heavier bullets in the K Hornet...
BTW... I experimented with swapping a 223 barrel ( 1 in 9" twist ) on a Hornet rifle ( chambered in standard hornet... at least to start with ) & had no trouble stabilizing 68 grain bullets in the Hornet case... sort of a mini 22 Whisper... I've since chambered that rifle to K Hornet, & though I'm loading outside the box, seem tro get nice results with 55 grain bullets...
BTW #2... chambering for K Hornet is easy, & regular hornet ammo can be fired in the K Hornet chamber to fire form... the hardest part about stepping up to the "K" is buying dies... I think my Redding Dies were between $60.00 & $70.00
BTW #3... I'm grateful for Hornady to release the 17 Hornady Hornet, as their cases chamber in my 17 K Hornet Contender barrel, makes forming cases for that cartridge much easier than forming them from 22 Hornet