As you said, only you can answer. Balance your list of perks, and add:
Pentax : constant f2,8, window for filters
sigma : no risk since you already have it.
If you want seals, a faster lens with a slightly wide FOV, go with the Pentax. I'm not sure the absolute quality of IQ will be better, as the Sigma is amazing. By the way mine does not creep at all.
If you enjoy the reach and weigth of the Sigma, and if you're happy with your pictures, then why not spend money on something else? (like a wide angle lens

)