spectra cord strength

Define "high winds"…. It'll work for a tarp that you set up in a well protected area even when windy.

High winds to me mean 60-90mph gusts on a exposed ridge – very little holds up to that and you wouldn't be sleeping well regardless.

How strong is the cord once knotted and in use for a while? Break strength is usually derated by at least 50% for working load.

How strong is the attachment point on the tarp?
How strong is the tarp?
How much pull can your stake or anchor take before pulling out?
Which do you want to fail first?

Adding to James’ comments:

And how much abrasion can such a thin line take?
(with memories of my Ti stakes abrading all my guy ropes in When Things Go Wrong).

Sure, such thin guy ropes will work under some conditions. Your safety margin will be a bit smaller than normal though.

Cheers

>Break strength is usually derated by at least 50% for working load.<
This depends on the knot that is tied. Some knots have up to 90% or more strength ratings.
I would not want to be the one testing a knot with spectra using my hands.
I use a knot tying Fly fishing leaders that is called a blood knot for good reason (yes I've proven the knots namesake)