Both the Garmin GPSMAP 8600/8700 series and the Garmin GPSMAP 7x3,9x3,x12x3 are high-end marine GPS Chartplotters with advanced features, but there are some differences between them:

1. Screen size:
● GPSMAP 8600/8700 series are offered in medium and large sizes:10, 12, 16, 17, 22 & 24.
● GPSMAP 7,9,12 x3’s are offered in the small and medium sizes: 7, 9 and 12

2. Screen resolution: 
● GPSMAP 8600/8700 series have significantly better resolution.
● For example the 8612xsv (8600 series) has a resolution of 1912x1080 where the 1223/1243 has a resolution of 1280x800 

3. Sonar capabilities:
● The 8600/8700 series offers Dual Channel Chirp, 70/83/200kHz, L, M, H Chirp
● The 7, 9, 12 x3 series offer Single Channel Chirp,70/83/200kHz, L, M,H Chirp
● The 8600/8700 series have an 8 and 12 pin transducer port for multiple transducers while the 7,9,12x3 have a single 12 pin port.
● NOTE: Only the XSV models offer sonar support, if you have a unit that is not XSV youwill need a sonar module.
● NOTE: The 8600/8700 17, 22 and 24 are non XSV and will need a sonar module.

Both of these options are great selections for your boat. Hopefully this helps you decide which model to