Hi Tony, I have the northstar 660, big brother to the 650 except screen size and higher pixels. Cant fault the Gps for ease of use and the sounder does a good job as well.
Just having a look at the specs the 650 is 600 watts and the 788ci is 500 watts, to me not an issue as you wont be going offshore. Both are the same screen size.
The hummingbird has much higher pixels making it easier to read. The combos in this size need all of the advantages they can get as the 5 inch screen split can be hard to read.
Either one would do the job you want well, but based on price and pixels I would consider the 788ci.
Cheers mal.