beauchampy,
I was reading off of a G-Raid 4tb, through eSATA to USB 3, averages around 175MB / sec and it was writing to my internal SSD, which averages around 1GB / sec. Don't think that the HDDs are the problem. I also, tried different combinations of drives, same gradual slow down after about 20-30 minutes.
But, I downloaded Resolve 9.1.6 and that fixed the problem. Now, it renders just under realtime (22.5fps), constantly. I rendered a 6+ hour render and it never slowed down. Screen saver was turned on and display sleep too. I also, was simultaneously surfing the net and watching some of the proxies as they finished. No slow down in render speed. I'm starting to think it must be a bug in Resolve 10 and / or something in Mavericks. I always forget that bleeding edge software is usually buggy.
Took me a while to find this, but here's a link to download Davinci 9.1.6 --
http://www.blackmagicdesign.com/support ... rue&os=macHope that helps you, until we get some sort of bug fix.