I have used pl380, K6, K3 and on Danley, Martin, VRX and Soundbridge Xyon. We did a test with all the amps on 2 Martin dual 18s with measured responce about 2 years ago for a buddy to decide which amps to buy. Running at 8 and 4 ohms the K3 and K6 were identical. The PL380 had a slightly lower impulse responce and peaks trailed off with 35Hz synth D&B playback. With a few seconds break on the lows the PL380 caught up but dipped again right away. I'll search for the Smaart screen shots. 4 audio engineers in the room could not tell any difference audibly. the K6 was picked since it provided more output down to 2 ohms. Benifits to the K series are setting the outlet current draw and peak voltage to the speakers. 17 pounds or so in a 1 U space is my biggest benefit. I have had my Ks in some pretty harsh hot environments and never an issue. Damping factor can be disputed if its really a benefit. Just keep cable runs short and dont go below 12Ga wire. I run my entire rig on two 20 amp breakers since going powersoft, no need for a distro anymore.
So basically decide what is more important since both PL and Ks performed really well, Size, Weight, dollars or a few extra features. Wattage differences never concern me anymore, a measure of work heat. The ability to provide constant current at a certain peak voltage at the speaker. I ended up with 2 K3s myself and very pleased with the investment.