i have a 6850 running off the new 3870k apu and i wanted to know if it would bottleneck what could be the positive and negitive spec wise if i did this vs triple fire the 6670
bottlenecks will be game specific afaik. check your cpu and gpu usage during gaming using windows task manager and a gpu monitoring program like gpu-z or msi afterburner.
there is no 'triple-fire' with amd apus. amd only supports 'dual graphics' aka hybrid crossfire aka asymmetric crossfire with cards radeon hd 6450, 6570 and 6670. some motherboards have pcie x8+x8 support but that's for crossfiring the two cards on the pcie slots, not for the apu and the graphics cards.
so i could not crossfire the 6850?
gta 4 bf 3 mp3 most new games on want to play all on max settings 1920x1080
imo you'll have to play them to find out. iirc gta 4 is a pc version of a console game which favors strong quad core cpus. your 6850 is not enough to max out very demanding game like bf3. but you'll be able to play at medium to high settings with reasonable fps as long as the 3870k doesn't bottleneck (unlikely with a 6850).
i have the 6850 and can run 90% at max but wanted to know if i could cross fire them since the apu turns into a cpu
if your motherboard has two pcie 2.0 slots supporting x8+x8 modes, then you might be able to run two 6850's in crossfire. however i suspect that the apu's cpu imght not be powerful enough to run two 6850s in crossfire. apus were designed to be run on entry level machines after all.