Circa 3K works well for SG2. I use a Naniwa 3k (really around 4k) which gives a nice edge.
Don't go to 3k until you can get a good edge off your 1k stone. Then use only light pressure with your 3k. A fine stone is for polishing an already sharp edge apex. It should only require light pressure coming off a 1k (you may need more pressure if doing a touch up on 3k only).
What kind of knives? What do you use them for, mostly? Do you have carbon knives you take to a higher polish? I ask because I think R2 can take a finer polish, if you're so inclined. But 4K is a great working edge for a wide range of jobs.