Every situation will be different. I know that when shooting BIF (and I’ve only been doing that for the past two or three years) I try to keep my shutter speed above 1/2000, preferably 1/2500 or better. When I was shooting BIF with my D500 I always used shutter priority and let the camera manage the aperture, and I generally shot at an ISO of somewhere between 400 and 1200, preferring to keep it at 800 or lower. Having read Steve’s guides, and now shooting with the Z9 where AF tracking is improved, I plan to shoot next summer with auto-ISO for the first time. For static subjects, the question becomes more of what are you comfortable handholding and what shutter speed is really needed. With the 500 PF without the TC, I would be easily comfortable at 1/500 for a perched bird or a wading birds that were standing still; for birds floating on the water it would depend on whether they were moving fast enough for me to pan or not. The TC is going to change things a bit…it not only magnifies your image, but any shake/vibration is also magnified. Take your time, don’t be afraid to experiment and learn from the photographers here while relying on your own experience as well. The more you shoot the more it becomes second nature.