I've got a 7 silver, I pretty much use it just on the boat. Takes great footage and easy to use, my only regret is I should have got the Black, can't change out the batteries in silver. I've used it to get underwater video of squid etc and still going good

 I have a 7 black, I prefer my old 5 black as the battery life was better, features between 5 and the 8 really aren't that different but the newer models chew the battery.

i place mine on my dash and have captured some pretty good fishing footage, great investment.

 Get an Osmo action, better and cheaper

 Get an 8 for the improved image stabilization.

Not that much different price wise ....... 

I purchased the Hero 7 Black before my holiday to NZ.

What an awesome piece of gear. Shits all over my sony sports camera.

Did all the extreme sports, jet boat, bungee jumping, zip lining, mountain carting and the footage is awesome.

I brought accessories off ebay some genuine (stick, head strap, chest strap, wrist grip, sleeve, backback clip). Just be careful some of the mounts can be a bit dodgy on the after market stuff. Always attach a safety line to prevent loss. I use an old iphone 5 as the remote control. Works a treat.

There are some settings to master / use for different filming but a few minutes on youtube and they are all explained.

I took three batteries, extra SD cards, and with a car charger and never had any problems. I also took a power brick and a 1.5m usb c cable to run it off the brick for long recording times if needed. Never used it.

Be warned it does get hot, very hot when recording with stabilization. The max recording time recommended by gopro is 15min on the highest res setting.

If it overheats it will shut down mid recording.

A 7 will do everything you want and more, without a good computer you won't even be able to view the footage at its highest quality. 
Battery life is average on high res, but that's something that you may not require, it improves in modes that will still look as good to the naked eye. Hypersmooth is excellent, especially when mounted to a boat. 
I am adding another GoPro to the quiver and for $200 ish cheaper I will get another 7. Improved stabilisation is great but you're looking at a narrower field of view and reduced battery life, also I can confirm the mounting bracket on the 8 can bend and ruin the camera. 
Either way, a few extra batteries will not hurt, they are pretty cheap these days (Harvey Norman was like $30 a battery for the 8).
If you're really tossing up and can't decide between them, what do you want to do with the footage and what exact uses do you have in mind?

My 7, like many others just freezes up all the time and you have to keep removing the battery to shut it down. Pain in the ass. My 8 is a machine, stabilization is awesome, image quality is same as 7 but seems more contrast has been added? 7/8 can get hot on extended shots so keep an eye on that.

My 7 has never frozen up in snow or sun but is regularly run till its out of battery while filming, maybe I've been lucky. Colours should be the same, but 8 has a higher bitrate mode maybe that's the source of the added contrast, I couldn't tell the difference when editing footage all shot at the same time though.
Key note is to buy the recommended SD card, had a mate wonder why he had artifacts all over his footage and first thing I looked at was his SD and I didnt recognise it. Sandisk Extreme V30 will do the trick, they're pretty cheap these days too.