So. I've got a 41 on the back. Because this is a bigger diameter sprocket, does this mean it's going to hold the chain further from the swing arm's magical 7mm mark?

Have at it SD boffins!!!

Yep...would look at setting it to 9-10mm. Just make sure there is sufficient slack or you will beat your gear box output shaft and seals into submission.

Actually you need to set it a little looser than 7mm, 4/5mm, the larger rear sprocket alters the chain tension more as the swingarm moves through its travel than a 38