I'll make this nice and simple for you guys:
Radeon 8500 LE = 230Mhz Clock Speed
Radeon 8500 OEM = 250Mhz Clock Speed
Radeon 8500 Retail = 275Mhz Clock Speed
If I had a choice retail is the way to go. This is my opinion from a once was radeon 8500 user and now I currently run a geforce 4 ti4600. At the time I purchased an original ATI made radeon 8500LE and flashed the bios to a Retail bios to get the cheaper card to run at the more expensive retail clock speeds. This worked without many issues. I'll be truly honest....my old Radeon 8500 blows away any geforce, including my ti4600, in color and contrast. I still miss the sweet sweet color of my radeon on my sony g400. As for speed yes I can now run all my games in 1600x1200 with my ti4600 but the color does not compare. Also like the others menitoned I dont get near the awesome quality in video and dvd playback with my geforce cards...sorry nvidia but you have alot of work to do in this area. I know they released a new cinema series addon but i still dont think it will help them beat ATI in the multimedia department. Don't get me wrong the geforce ti4600 is a great card and not to mention expensive...but if i didnt get the card given to me as a gift I would never have traded in my radeon 8500 running at retail for it. And I'll be sure to let you know when its up for sale when ATI releases the R300.
My opinion, my views, my experiences......
PS: To answer the threads question...with the decent machine you are running defintely get a new vid card over a game cube...consoles are for little men especially game cubes. And if you want to choose a Radeon 8500 I say stay away from all third party Radeons at this time and stick with an Original ATI made Radeon 8500 retail. 64Mb is fine if you can still find a retail but you may be forced to the 128mb model. There is a huge dif in speeds as you can tell what i pasted above so if your wondering why an LE or even a OEM is that much cheaper that Retail...this is the reason why.
Peace