Not a big fan of DO and mirror lenses, image quality isn't good enough.
I could bring my 300 mm f4 in, combined with a 1,4 extender I'd still have 420 mm. Add the old 20D with that which has a 1,6 crop and it should be quite ok. Downpoint : dragging another camera and lens with me ... this year at Sebring I had already 18 kgs of camera's and lenses on my back and as hand luggage on the plane 
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Anyone been before at St Pete for a race ? Would like to know whether there are good viewing points without a fence in front of you.
The only downside to that plan is that you need to be able to guarantee bright sunlight to make your 300mm f4 any use.
I've decided less is more for Sebring. I took a 300mm lens out there (1.6 crop), and even from the public viewing areas, I didn't really feel the need to use it. Surely out there you only need a 70-200mm f2.8 and a 24-70mm for the campsites and pit lane? and maybe a 1,4 extender??
As for DO - I don't think "likes them" per-se - they're just a convenient package for circumstances such as this - I have a friend who swears by them for getting his camera into gigs that he wants to take photos at too. I've never really used one - well not that I've seen the results of anyway - but reviews suggest that barring a little Chromatic Abberation and a little vignetting on full frame cameras, the lenses are not all that far away from Standard L Series glass..... Like GF, I also find the technology fascinating - but in contrast to that - I'd see the effect of using the off-axis light on the Fresnel as an opportunity to exploit the oddities of the lens, and make images that nobody else could.....whether it would work or not, is a discussion for a photography forum though
