The problem is being confronted with the difference every day.
I'm shooting the Tam as were it a prime since it takes a whole lot to fill my frame and that forces me to shoot her at the long range most of the time. I have her about always at 400 right now but each time I upload the shots and go through them, I am not very satisfied. That's not because of this Tam but because of the other. My 200mm micro is as sharp but she's too slow to use for birding so I wasn't as often confronted with the differences.
I'm checking the used market here but long primes aren't for sale that often. If you got one, you usually keep it or already know someone that wants it. I also don't feel like going to the gym six days a week until I can shoot some primes handheld. I don't like dragging along a pod for birding.
April is only some weeks so I will give it until then and if there is no word about the 300mm, I'll pick another and be done with it.