Note that you cannot put a 604ev (250-350MHz) in a plain-Jane 8600. There are two 8600 logic boards, the original and the "Kansas." If the badge on the front of your machine reads 8600/200, the fastest card that will work is probably a 233MHz 604e. If it is an 8600/300, you can put a 350MHz 604ev card in it (originally a 9600/350) — and they can generally be overclocked successfully, one advantage of the 604ev being that it does not get nearly as hot as the 604 or 604e.

I have a couple of dual 604e machines, as well as 604 and 604ev models. A 604 or a 604e can be put in most any machine. A dual 604e without cooling gets too hot to handle, and really can burn your fingers, so it can really only go in machines with a fan, like the 9500, the 8600 and the 9600. A 300MHz 604e without cooling just gets pleasantly warm. I have run my 8600/300 for years with no side fan in order to cut down on the noise. Overclocked might be a different story.