Yes, 12k to Jnats & have also jumped from 5k to Jnat's. Also been using 5k to 12k with no 8k pro. The 12k is plenty fast to make the jump. Don't have the 16kGS only 8kGS. Used to use Suita to Asagi after 8k GS.
1k pro is a killer on stainless or tough carbon razors for bevel set but I usually use the 1.5k on edges that don't need a lot of heavy lifting. For badly pitted & chipped bevels I may even start at the 320grit & always go to 1k from there.
Never bought a Chocera 1k. Tho I was curious, just never felt the need. I only have experience with King 800 &1200 & Shapton 1kGS & Kasumi 1k to compare but as much as I liked the GS, they just sit neglected atm. The 1k J pro is faster & holds it's flatness better than any of the 1k's I've used.