I've got three .308's right now, a Saiga .308, a Remington LTR and an Ishapore 2A1. I'd also like to have a light sporting bolt action in .308. It's a great all around cartridge.
Accuracy wise, the Saiga is fine for deer hunting within 200 yards, but it is easier to shoot accurately with a good bolt action. I agree with the post above where typical accuracy was about 2.5 MOA for a Saiga and 1 MOA for a bolt action. You probably will have to spend awhile at the range however to figure out what ammo will deliver those kinds of groups. I've shot some stuff out of my Saiga that only grouped about 6" and I've shot other stuff that grouped under 2". My LTR on the other hand is a tack driver even with bad ammo. My worst groups off a bench with it have been around 2" and my best have been less than 1/2" at 100 yards. With good ammo it will consistently shoot less than 3/4". An LTR is an unusually accurate bolt action however.
For hunting deer at 150 yards or less however, your Saiga x39 will do the job pretty darn well. A good bolt action would be better, but the Saiga's plenty adequate.