I agree with Hans (hnikesch). I can handhold up to 300mm (1674mm EQ) with the Q and adapted lenses with shutter speeds as low as 1/100 with SR, but to get really good sharpness 1/300 or faster is better. I've also found that though a faster prime (300mm f4-4.5 @ 2 lbs) has better IQ potential, a lighter (one lb) slower (f5.8) consumer class zoom like the DA 55-300 can work a bit better than my premium primes for handholding because of the lighter weight. I think the limit for any individual is depends a great deal on technique
https://www.pentaxforums.com/forums/pentax-q/204091-q-fw-v1-1-da-55-300-handheld.html
If you scroll down in this thread, there are pics of my setup. The Hood Loupe is an important accessory to shoot long lenses handheld with the Q. It allows me to brace the camera against my face, like a camera with an eye level viewfinder, and this contributes to steadiness considerably.
Also, with the OEM Pentax K to Q adapter, there are 3rd party tripod collars that can be modified to fit the adapter. This has a couple of advantages -- lower cost and the ability to rotate the foot of the adapter to change the orientation of the camera to the foot.
https://www.pentaxforums.com/forums/pentax-q/208945-chinese-tripod-rings-pentax-k2q-adapter.html
In my experience, the rolling shutter (jello effect) from the electronic shutter and 3rd party adapters does not significantly effect the image unless the motion (either camera shake or subject motion) is pretty fast, so this is not really a major consideration for me for stationary bird shooting. If the motion is that quick during the exposure, it would produce blur in the shot anyway, even with a mechanical shutter, so this is really not an additional factor for me to account for when shooting, but knowing that the actual exposure is taking longer to complete than the indicated shutter speed means that I "follow through" with the shot, holding the camera on target as steadily as possible for a bit longer than I would with a DSLR or with the mechanical shutter equipped Pentax adapter.
Scott