DefMunky - My advice, FWIW, is to keep putting the Yamashins to work and then evaluate what you'd be looking for in a larger and/or higher-end knife.
What do you like/dislike about the Yamashins after some use?
How do they work, dicing onions? This is a fairly good test of the front 1/3 and tip of a blade (assuming it's sharp).
Do you like the edge profile during use?
How do you cut product - push cut, push-glide, rocking, chopping, etc.? This can influence what type of edge profile you might best suit your style.
Are you looking for a very light, thin laser type knife, or more of a middle weight with some backbone and very thin at the edge?
Do you already have a longer (9"-10") knife for tougher tasks that can take some abuse? A Wusthof, Henckels, Victorinox, etc.
I don't know the balance point on your Yamashin Santoku, but think about your grip - do you pinch grip or use a racket style grip? This can dictate whether you want a knife with balance point nearer to the handle or more weight forward. They can vary considerably.
I'm sure there's more that others can add, but thinking about these things while using your existing knives will help pinpoint what might work best for you on a more expensive purchase - helping to get it right the first time.
These knives are all really good, but they have different characteristics - we want to help find one that fits you to a tee
If you have the room in your kitchen and on your cutting board, I'm still going to suggest a hard look at 240mm Gyutos. I'm afraid that a 210 might not be enough of a jump from your 165 Santoku. If you like the flatter blade profile of the Santoku and it fits your cutting style, then you should look at a flatter 210 or a 240, as they usually have a longer sweet spot for push cutting. It also depends on the size of the products that you prepare as to what size Gyuto might be best.