Your lenses are good ones. As you do significant cropping at times, the 24mp of the KP will be very advantageous. Yes, not having the AA filter alone makes a difference. No current Pentax DSLR models have an AA filter. You could indeed wait to see what the forthcoming new APS-C flagship might bring, but keep in mind it will likely be introduced at around twice the price of the current KP offerings. Then you could wait about another year for the price to settle down some- maybe at around $1,000 or so. Also, since you are coming from a K-30, not a flagship model, you will not miss having a top LCD screen etc, so the additional features the KP brings you will be well above those of your K-30. Its set of controls is very advanced and useful. Also keep in mind these models (KP, K-3, K-5, etc.) are designed for use by pros and other advanced photographers, so they do not include the "Scene" modes. Instead you get better controls with the KP to bring about what you need when facing various lighting challenges, once you learn when and how to use them and what to do.
Due to your location, stores offering great prices for a KP, like B&H, are located relatively close for you. But I don't necessarily recommend that you "go and hold a KP to see how it feels to you". It will of course be somewhat different than what you are used to. I am assuming by your statements that you don't have a hugely deep background in camera use, as many of us here are very experienced "holders" of many different cameras with a variety of sizes and designs, yet we have and love our KP bodies. The idea is it might take you a little time and experience to adjust to a different design concept. In so doing, you might improve your holding technique and along with that the clarity of your results. For stability, even with SR, you are better off to hold with the left hand from underneath providing most of the support, while the right hand is for additional stability and to work most of the controls. This is far better than holding as if grabbing someone by the ears and relying on a large right hand grip.
That said, when working with large lenses for hand-held shooting, a bulkier camera body helps for handling the camera for a period of time during a lull when not shooting. When shooting with such a lens, holding of the lens itself from underneath is the standard method, so the body's right-hand grip is of little consequence while shooting. I have the FA* 300mm f/4.5 which is lighter and more compact than your very fine M* 300mm f/4, but still quite a large lens. With such a lens on my KP, I find having the optional battery grip provides a better balance for general handling. You will then have loads of gripping surface, along with loads of battery life. And as to overall weight, about the same as a K-3 II flagship with no battery grip, yet with even more battery life. With the advantage of such low prices now for the KP here in the US, the battery grip at about $198 still puts the entire cost well below what the new flagship alone will cost.
The KP will afford you numerous advantages beyond having 24MP for cropping. Its low light/higher ISO performance for higher shutter speeds for hand-held shots or live subjects is outstanding. This will allow you to increase your ISO more without significant loss of quality. When shooting with a 300mm lens, even with SR you will need more shutter speed to ensure clarity.
Even with JPEGs right out of the camera, the KP's processor brings exceptionally great results. Just be sure to set up "Fine Sharpening" in the Custom Image menus, especially for the most often-used "Bright" category. Important!
Last edited by mikesbike; 12-11-2019 at 04:04 PM.