The 800/8 can be a good choice, depending on your application. But running it in 8-channel mode would not be my first recommendation for dpolen's application.
The reason is this...the 800/8 amplifier will put out 75 watts per channel at 4-ohms, 100 watts per channel at 2-ohms and 200 watts for 2 channels bridged into 4-ohms.
In dpolen's system, that would give him 75 watts to each of the 4 in-boat speakers (Channels 1,2,3,4) which is good; 200 watts to his subwoofer (Channels 5 & 6 bridged) which is good; but only 75 watts to each of his tower speakers, (channels 7 & 8) which is a bit underpowered for the JL Audio MX770 or M770 tower speakers IMO. I like to power tower speakers with a bit more power than the bare minimum because you're typically asking the tower speaker to play quite a bit louder than the in-boat coaxials.
So while the 8 channel amp does seem like the perfect all-in-one solution, I think he can get better performance with the 700/5 and 400/4, although at a slightly higher cost. If the budget is the main concern then the 800/8 will work, but at that point the 700/5 will give similar performance at even less cost.