Does anybody have some advice for me here? My OPO isn't on it's deathbed, but it's close.
I think similar to the comparison with the Pixel 2 further up (though the 5T has better performance and battery than the Pixel 2), I'd have to give it to the Note 8 by several orders, though as far as I can tell the Note 8 is a fair degree more expensive.
Note 8 has;
+ A much better design, with a better screen to body ratio.
+ A bigger screen.
+ A much better screen in terms of peak brightness, colour accuracy, colour gamut and resolution (1080x2160 vs 1440x2960).
+ HDR10 (already works with Netflix etc) plus 3D Touch.
+ Better performing cameras front and rear despite lower megapixels (bigger sensors and lower aperture on front for improved low light).
+ Dual type cameras (one regular, one zoom), both with optical stabilisation, plus a better portrait mode.
+ Better split screen multitasking and features.
+ A stylus with Wacom screen tech for added productivity.
+ SD card slot for expandable storage.
+ Wireless charging.
+ Waterproofing and dust resistance (5T has neither), so you can comfortably use the Note 8 in the rain or not worry about getting it wet, even using it in a swimming pool.
+ A better internal DAC/Amp, useful if you plan to use a wired earphone or headphone, especially audiophile grade.
+ Compatible with Samsung Gear VR and Dex.
+ Samsung pay (best mobile pay tech yet).
The Oneplus 5T has;
+ A much lower price.
+ Slightly better battery life.
+ Quicker charging.
+ Ever so slightly quicker performance (though both are essentially the two fastest phones on the market).
Really depends on what you're after or what you need. The Note 8 is a better designed and far more feature rich device, whereas the 5T is a more streamlined, affordable power house.