Newegg is sold out of the rebadged 6770 that would install Lion/ML without any voodoo
It runs FCX very well->
http://www.newegg.com/Product/Product.aspx?Item=N82E16814105003
The rest of the 6770's have been hit or miss on installing ML...
However, I found this->
http://www.serversupply.com/MULTIMEDIA/GRAPHICS CARD/1GB/DELL/GCJ42.htm
It looks like the XFX version that I have and they have identical performance as the 6770's
Haven't tried these from server supply yet, I'm trying to make up my mind about getting into nVidia 6 series as I think the 5770-6770 is at the end of life.
I have 3 of the XFX 5770's and 2 of the HP 6770's in service that are ML/FCX hacks...THEY JUST WORK!
It just depends on which 6770 you have and how many displays you want...but if you can USE 3 HDD setup:
1 for content, 1 for import and 1 for render (can be your OS HDD)
I use HDD for content/storage, SSD for import and SSD for render and this setup is brutally fast