Any fan spinning faster than 1000rpm is too loud, and a 70mm fan spinning that slow isn't going to push enough air. Also there are tonality issues with 70mm fans. Finding quiet 80mm, or 120mm fans is much easier. The bigger the fan, the slower it can spin and still give proper cooling. Personally I don't run any fans over 800rpm in any of my systems. Also all stock GPU heatsink/fans are too loud, hence necessitating some sort of aftermarket cooling. All aftermarket air coolers I can find are 3 slot solutions only. That all said, my biggest hurdle has always been finding the right sized enclosure, and your enclosure is as close to the perfect size I've been able to find. I can always just buy a riser card one slot higher and mod your chassis to fit it. There appears to be enough vertical clearance for it to fit. Then just use a 4.75" hole saw to cut fan holes in the top and bottom. I'd probably want top and bottom panels without vents so the final product looks clean. I'd rather have wire fan grills than stamped vents in the case panels.