#1. "RE: Canon 77mm 500D option?" In response to Reply # 0
Rather than look for new equipment, I'd just work around the problem. If it were me, I'd first work on the vignetting in Lightroom. If that isn't sufficient, then I'd start framing a little looser and cropping. Unless you have to make a 24x36 you'll have plenty of cropping capability - and if you're printing on most standard paper sizes you'll need to crop some anyway.
None of your alternates is going to come close to the optical quality of the 300/f4 AFS with tubes.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!