8mm fisheye vs 7mm fisheye?

1) vivitar 7mm fisheye = $315
2) Rokinon 8mm fisheye = $280

A have a cropped sensor DSLR (Nikon D200) So I want to get a wide as possible.

My question is, is the 1mm really that much of a difference? And If you had to choose, which one would you get?

Added (1). Thanks Todd, But I'm on a VERY tight budget, and the cheapest Nikon fisheye lens is the 10.5mm for $775, and that would make it a 15.75mm on my D200… So I can't afford it, and it's not what I want.

Honestly I would get the better of the two… 1 extra mm may make or break your photo… And you will never say "man I wish I got that one with the extra mm"

Also. I would go with Nikon… I would never buy a Vivitar. It's like buying a Farrari and putting cheap tires on it!

Then go with the Vivitar 7mm