Thanks guys, really appreciate the input. I know falloff happens to all 90s, but I'd rather pay ~$200 for a center filter that $$$$$$$ for the 10000000mm filter for the XL. I haven't seen any tests, I'm still getting my feet wet in the intriguing LF waters. Good to know they're all sharp. I have the Nikon 65mm, and it's great, but the movements are so limited. I'll keep poking around and see what I find.
Thanks all! Other perspectives still welcome.