You already received some good advice from experienced Pentaxians.
In my opinion, I would not bother to change lens for so little focal length range difference (only 10 mm), unless you absolutely need a WR all-around length that you will use heavily during your next trip/adventure.
Instead, I would recommend to save the money and consider to invest in some prime lenses.
Your sigma lens, like every zoom lens, is a compromise over the focal length range. In comparison, a prime lens (ie single focal length) is optimised and will give you, typically, a much better IQ for the same price. Many Pentaxians have a series of lens incl. zoom lense and prime lenses. The IQ of some prime lenses is extraordinary and you can be easily hooked.
Hope that the comment will help....