My only concern is that I see the gpu hot spot get into the 90°C to 92°c range when gaming.
The hotspot sensor (as one can assume) returns the hottest spot of the entire die. Since vega AMD has put some sensors inside the die, and of many this is the hottest spot. Nvidia perhaps has this feature too to control their boosting algorithm but does not show it to the user.
Am I being worried over nothing?
TL;DR
Do not worry about if it is below 100°C.
90-95°C is fine here if you only do gaming. For mining (or other 24/7 task) lower TDP for lesser temp, or undervolt. AMDs stock coolers take them for low level gaming beyond 110°C. Acually it stops there, but the GPU will throttle then.
Longer explaination:
The Navi 10 XT Chip (on 5700 XTs) is a very small chip 251mm² compaired to (for example) a vega 10 xt chip (on vega 64) 495mm². I got both so I can draw some conclusions:
Both have 240W TDP (both Sapphire Nitro+)
Navi10 chip has a power density of ~0.96 W/mm² | (Surface per watt 1.05mm²/W)
Vega10 chip has a power density of ~0.48 W/mm² | (Surface per watt 2.06mm²/W)
(Yes I know, not every watt is going to the GPU die, but a high amount of 150-200W if needed)
Therefore the coldplate from the cooler can collect the ermitted heat better (because of more surface and therefore more surface per watt). Vega64s hotspot is usually 10-15°C ahead from the normal GPU temp sensor, even at 300W TDP. (I also can not tell if the Nitro+ cooler on the vega is just better, it is however bigger)
RX5700XTs Hotspot is normaly 15-25°C higher than the GPU temp sensor. As said this mostly comes from the more compact chip.
Should I be going this route or should I stick with wattman?
I was afraid of this sensor too, so I found out that I can undervolt my GPU and still rase the GPU clock to wattman maximum. I do not like Wattman because it resets randomly. I recommend MSI Afterburner.
Stock 1200mV Vcore, 2070 MHz Core, 1800MHz mem.
Do not touch mem! You can really brake the GPU by touching it!
I started messing with undervolting today
I recommend to try lowering voltage (-10mV steps) until the temperatures fits your needs (as said, everything below 100°C is fine for gaming). Use Unigine Superposition to test it (as example for a gaming-like benchmark) because you want to keep track of your performance as well. Lower core frequency only if it crashes. Some games however (Tomb Raider/ Unreal games) can still crash. Then just quickly lower core frequency a bit to continure gaming.
If you are done with optimising temperatures and you did not have to touch the core frequency, you can still try to increase it (slowly). But that is voluntary extra work.
I got stuck flashing the new bios back to the card.
I see no reason why to flash a 5700 XT. You have an unlocked GPU. Also flashing can destroy that thing quite fast.