Those fans arn't really made to do that job, though depending on your container size, a few of them WILL get it done nicely. Just 1 is testing it IMO. What you really want is a centrifugal fan; 300+CFM, and made to overcome static pressure; loud and overkill mostly. The most well respect brand for quietness is Can-Fan.
But only 8GPUs you should be fine without that. Keep your gpu box as small as you can, another duct booster and you should be fine.
Anyways I'm going to try and get by with these $30 6" duct fans. If that won't pull enough hot air out then I'll look to bigger setups but will consider price. I'll know by the end of this week.