OP here. Okay I checked the seat height, but it was at the default "L" position as I expected -- the guy I bought it from barely used the bike, doubt he ever took the seat off, heh.
Measured the old Ninja, approx 29" at the lowest then when sitting on the bike it sags somewhere in the 28-28.25" range. (Probably needs a new shock after 10 years? But only 9K miles.) Like @KSK says, I am all sorts of flat footed there, more than enough. The Ninja may be a bit narrower also. The sag is probably even a bit more than that, due to the way I measured it with my body more towards the rear than in the saddle.
The FZ6R measured about 31" but I couldn't get a reading with me on the seat. No place to scoot back like the old Ninja's banana style seat. However it's pretty obvious my thin frame barely deflects the FZ6R shock, so I lowered the pretension from 3 to 1, which helped a little. It's not that I can't flat foot, but that I pretty much have to be positioned just right, no wiggle room. Legs straight to the ground, no flexing.
I'll have to decide between the Soupy 1.5" link (or PSR), Roaring 1.75" link, or that other 2" link (T-rex, eBay noname.) I am a little worried about overdoing it. And a new kick stand too ...