Upload & Sell: On
Some 400 prime versus 100-400 zoom discussions on the last couple of pages over at MA2A. Start on this page:
That's my post with a series of images I shot with the 100-400, and the race cars were at Lime Rock.
My vote is for the 100-400. I love mine. Part of the reason is the versatility, but also because I think 400mm is probably too long 90% of the time at Lime Rock. I shoot there regularly, and I don't even bring the 100-400 anymore. I use a 70-200 for just about everything on the track. Galleries are here:
(Edit: I just noticed you live in DE, so maybe just happened to be at Lime Rock and it's not your regular track. Still, I use my 100-400 for baseball, soccer, air shows, nature, and even dragonflies and butterflies. It's a great, versatile lens. If I ever buy a 400 prime, I'd still keep the 100-400.)