If your thinking about going to a 698 then save yourself some money and go 598 si they are the same as far as specs and screen size and transducer. go to Acadmey they have them at 549.00 the 698si is 699.00 3 weeks ago acadmey had the 598si down to 449.00 thats when I got mine. but check out humminbird website you can see the specs for yourself, the 598 is in the closeout section. and I think that is the reason because there the same as the 698
The 600 series replaced the discontinued 500 and 700 series.
The 698 has a narrower display which is what you do not want in a unit that does side imaging.
The 598 and 798 have the same display size.
In all cases, a wider display is preferable for side imaging.
500 and 700 series is better than a 600 series
800 series is better than a 500 and 700 series
900 serice is better than a 800 series
1100 series is better than a 900 series.
BIGGER is better