I hunted for years in x-static based synthetic base layers. They seemed to do well on multiple day outings. I also regularly use Wildlife Research Scent Killer. this last year I switched to a merino base layer and the first thing I noticed was that my merino was more comfortable and not as scratchy. I only have two early hunts in full merino, so I'm by no means an expert with it.
You will be able to go longer periods with not washing merino over the syn stuff. No matter what they do to the syn it always stinks up sooner plus the merino is better at regulating temp then the syn.
I have used the syn with silver and it still started to get ripe after a few days.