A 610 grain arrow is a little less than 12 gpp, which would be common for hunting larger animals like those that have antlers like the ones your bow is hanging on. Is that a red deer, and did you shoot it?
For hunting small game or target practice, you might be happier with arrows of about 9 gpp, which would be about 468 grains, and should increase your speed.
My older K4 was given to me by a friend who knows I like classic old bows. It was very harsh to shoot with a lot of hand shock. Perhaps some heavier arrows like those you shoot would tame it down some, but I never tried it with arrows that heavy. If you do try yours with lighter arrows, I would be interested to know if it remains smooth and quiet.