Just getting back into gaming and want some advice on how to setup my system. 
I have a EVGA RTX 3080 FTW3 Ultra and running a OC 450W bios. Bios has flexible BAR capabilities, should I use this flexible BAR for Halo?
Is Halo going to utilize ray tracing?
Should I use my monitors G-SYNC?
I'm running 1440p/120FPS on ultra settings and it runs pretty good. 
MSI AFTERBURNER: have been at 118% power, +90/+800, forcing constant voltage. Think my temps were like 81* on Halo. Curious how this might compare to another gamer. 
My PC has a 8 core AMD processor. 
I can run +1200+ on memory overclock but I get a lot of horizontal blur lines. Still get some even with no overclocks. IDK if undervolting is a thing for me. Thanks in advance for any advice

I like gsync.  Just make sure you cap the frames to like -2 of your monitors max refresh rate and turn on vsync in nvidia control panel.

Halo Infinite should get ray tracing sometime and it's probably best to enable BAR for it since it's a modern game.  In any game using G-Sync is going to give you the best image but make sure to disable vertical sync.
 
For the horizontal blur lines do you get them in other games or benchmarks when it's at the default settings for both core, voltage and memory?

I turned on Gsync and Vsync for Halo and my blur lines (screen tearing?) are completely gone, now, very happy now with this card and performance at 1440/120
I bumped memory oc to 1350 and so far so good. 

Wish I could turn up the core more but it'll start crashing Halo Infinite, really want to water cool after seeing how my hybrid 1080Ti performed. 
 

MXHALOFAN
Wish I could turn up the core more but it'll start crashing Halo Infinite, really want to water cool after seeing how my hybrid 1080Ti performed. 
 

I've really come to appreciate the VRR and Gsync on the 120hz LG OLED I have. Not having to bother with messing with vsync between the range of 40-120 means pretty much everything runs smooth.

MXHALOFAN
I turned on Gsync and Vsync for Halo and my blur lines (screen tearing?) are completely gone, now, very happy now with this card and performance at 1440/120
I bumped memory oc to 1350 and so far so good. 

Typically you want G-Sync on and V-Sync disabled. G-Sync should make the frames render every frames as fast as the GPU can produce them unless you hit the 120Hz to top out the monitor you have. With V-Sync turned on some games will render based on the 120hz. That means you might only get 90fps, 60fps or even 30fps if frame rates drop below 120fps. A lot of games disable V-Sync if G-Sync is turned on.

Hoggle

MXHALOFAN
I turned on Gsync and Vsync for Halo and my blur lines (screen tearing?) are completely gone, now, very happy now with this card and performance at 1440/120
I bumped memory oc to 1350 and so far so good. 

Typically you want G-Sync on and V-Sync disabled. G-Sync should make the frames render every frames as fast as the GPU can produce them unless you hit the 120Hz to top out the monitor you have. With V-Sync turned on some games will render based on the 120hz. That means you might only get 90fps, 60fps or even 30fps if frame rates drop below 120fps. A lot of games disable V-Sync if G-Sync is turned on.

The advice from blurbusters with G-Sync, is to enable vsync globally, cap your frame rate at ~3 FPS under your max panel refresh rate in the NVCP and disable vsync in the game menu for the lowest lag and smoothest frame rate in the range of your panel. In this way you're not going to see the drops to 90 60 or 30 when you're using G-Sync. Your panel should be synced through out its range.
On my LG, set up as above, the G-Sync range is 40-117 hz. Pretty much every title I have will run in that range at max settings. You don't have fixed refresh rates, it varies smoothly within the range, with NVCP vsync on.
 

I have a GPU Performance Cap going on in my sensors tab in GPU-Z. Says Reliability Voltage and Max Operating Voltage (shows this in history during gameplay). Curious if this is caused by "forcing constant voltage"? I have my Voltage set at 100% (max setting in Afterburner), 118% power
My pin #3 wattage is like half what Pin #1 & 2 values are. Does this card require a shunt mod or something to get all three pins power # in line? Love to sort this out and get more core OC, +90 is ok but it'll crash Halo with anything higher after a few games etc. Plays amazing at like +130 but just won't stop crash and really want that # OC lol
Thanks in advance

3rd connection reading less power is normal, nothing you can or should do about it. If you're not happy with the performance, sell it and get a Ti. I don't know of many cards that will be stable for gaming at more than +80. That's about the limit with the ones I have tested, pushing memory that high can also cause a performance regression, it will run but it will not perform as well because of Error correction.