In reply to andrewmcleod:
> But 8mm dyneema is massively less bulky than 8mm cord, so not really a fair comparison. Would anyone seriously use a 4m cordalette in 8mm? :P
I notice my 10mm 400m dyneema sling is about 15g/m, which would indeed be 4-5mm. I suspect the most commonly advocated nylon cordelette diameter is 7mm, which would be over twice the weight when dry.
(Bluewater cord...5mm=16.5g/m, 7mm=32.9g/m)
It's difficult to know how much strength reduction you'll get, if you do the common 3 piece cordelette thing you'll end up with a big overhand with 6 strands running through it. The test results you see tend to be for a 1-2 strands of material so don't really apply.
RE: Screw gates, while I have and a few, but I don't think you need more than 1-3 (1-2 if you don't use guide mode). Screw gates are heavy, I'd get the lightest you can (Petzl Attache 3Ds & WC Neons perhaps.)