22/06/17 EDIT: This has become my favourite quadcopter to fly. Not on 5" but on 4" props! The power to weight ratio is amazing with a 600mAh 4S and it's a very fun quad to throw around. I've also since designed some camera mounts which bolt on top of the flight controller stack:

HS1177 FC Stack Cam Mount: https://armattanproductions.com/pages/kit_detail/1009

Runcam Swift Micro Stack Cam Mount: https://armattanproductions.com/pages/kit_detail/1008

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This is a super light, super simple frame designed for 5" props, but with a twist - 1306/1407/1707 motors. 

I've seen a few people try this combo, specifically the Tornado T1 1407 3600KV motors on light 5" props. 

Here is an example of what I'm talking about:

https://youtu.be/ELsv0kbN3cE

It seems quite a few people are modifying the twig frame to use these small motors, but I've drawn up this custom frame to do the job instead. The arms are 4mm thick and 6mm wide. The 2x middle plates are 1.5mm thick, so I'm not expecting strength to be an issue here. It's motor to motor distance is 200mm. I haven't designed a top plate for this frame in order to save weight and cost. I have had questions about how to mount the FPV camera, personally I plan to print out this mount for my frame: http://www.thingiverse.com/thing:1441375 

Another great camera option for this frame would be a "tiny whoop" style camera which you could tape/glue/rubber band mount on top of the flight controller. Example: http://www.banggood.com/Eachine-TX03-Super-Mini-025mW50mW200mW-Switchable-AIO-5_8G-72CH-VTX-600TVL-13-Cmos-FPV-Camera-p-1104884.html?rmmds=search

I've designed the bolts that hold the arms on so the outer bolts are 30.5mm apart so you can mount a standard FC, and the inner bolts are 20mm apart, so you can use one of the smaller FCs and 4 in 1 ESCs that are coming out on the market. 

Check out my video of this quad here: