Ive been staring at spec sheets for three days straight and my head is actually spinning. I finally upgraded to the R3 because I wanted that insane autofocus for my trip to the Everglades next month but now Im paralyzed by the lens choice and honestly its making me regret the switch a little bit. I spent all this money on a pro body and now I cant decide if I should go native RF or stick with EF glass.

I read all over the place that the RF 100-500mm is the gold standard for the R system but then I see people complaining about the f/7.1 aperture at the long end and it scares me. I do a lot of shooting at dawn or under heavy tree canopy and I feel like f/7.1 is just gonna turn my images into a grainy mess even with the R3 sensor. Then I looked at the EF 200-400mm f/4 with the built-in extender because some pros say its the best zoom ever made but its like carrying a literal boulder and the price for a used one is still eye-watering. Plus I dont know if the adapter adds lag to the AF? Some say no some say yes and I just want a straight answer.

Here is what I actually need to make this work:

• Budget: I can stretch to $4500 if I sell my old kit but Id prefer to stay closer to $3000
• Weight: Im gonna be hiking 5-8 miles a day so I cant carry a massive prime lens setup
• Reach: 500mm is the minimum for the small warblers Im tracking
• Speed: I need something that wont hunt when the sun starts going down

Is the 100-500 really okay in low light or am I better off getting an older EF 500mm f/4 prime even though its not a zoom? Or is there some middle ground Im missing like the Sigma 150-600 with an adapter? Ive heard mixed things about Sigma pulsing on the R bodies though and that would drive me crazy. I just want to stop researching and actually buy something so I can practice before my flight...