Digital photography

anyone have any experience with the Canon 1Ds Mark 3?

i'm looking to invest in a full frame camera at some point, i currently shoot with a 7D i do use the 8fps which is the reason i was looking at the 1Ds

does anyone know what mm fisheye lens they will take before they start producing a circle?

Yes, used 1Ds cameras of all kinds for years. You're paying for the tank-like build and reliability of the body and shutter basically. Bear in mind that the Mk3 has been out a long time (over 5 years) so if you have to borrow money to buy it, it won't be anything remotely resembling an 'investment'. Not sure it's even available new here (USA) as the 1DX appears to have 'superceded' it.

As for your Fisheye question; A lens is either designed as a Circular Fisheye, or it isn't. The camera body is practically irrelevant.
Canon's 15mm f2.8 isn't a Circular, but the shortest end of their 8-15mm f4L zoom is.