I have about a 6.8 inch wrist for reference. I'm still happy with how it fits. It's a big watch though, no beating around the bush there. And I won't lie, I wish Seiko had reduced its diameter and lug-to-lug by 1mm-2mm. But as others have said, the case has been designed smartly/ergonomically; the watch doesn't appear as big as its stated 43.8mm diameter, and there's enough curvature to the case for the 50mm lug-to-lug to wrap around your wrist decently. With that in mind, I would think that the watch would fit pretty decently on your 7 inch wrist.
As for the movement, the 6R15 in mine currently runs around -10 s/d, which is a bit disappointing considering the price-point. Others have reported better performance from their 6R15s, so unfortunately it's still luck of the draw there.