Garmin gpsmap 7612xsv or 7612?

7612xsv: https://youtu.be/MPx5oLo8Z4s
$1699

7612: https://youtu.be/Q0QkscGOJNY
$1499

To buy two different ones or to buy two identical ones?

Well sort of depends.
The Xsv will have your maps,sonar and si/di which can link to the 7612 so you should be covered.
Only downside I see is the resale value on the none xsv will be less and harder to sell if you decide to do so.