If you want to push the long range aspects of the .223 you will want to use the heaviest bullet you can.  Using a heavy bullet needs a faster twist, so that would point to the 1:8 choice. 

Both of those scopes have a pretty high magnification on the low end so that's going to be a problem when used for hunting, ( from my experience )

We LOVE our 8 twist 223's!

Also to consider is the weather , if the varmint is a stainless steel barrelled one it should stand up better to the weather over here in England imo

Get the 1-8 twist and don't look back.

Tac with the 8 twist.

I'm very happy with the 1:8 twist on my Sporter .223

I recently found and bought a batch of JLK 80 & 70 gr. VLDs at an estate auction and look forward to some long range load development.