Help deciding on a setup for home

Hi,

I'm looking for some advice on the best setup for my home. My router is downstairs (currently a Super Hub 3) and my office/game space is upstairs at the other end of the house (it's not big but the walls are thick). I was using a powerline adapter originally but the speeds were awful. I recently purchased the AX8 extender and have been using to connect my PC and NAS to the internet and allow my laptop to connect to an access point that had a Gigabit connection to my NAS (while also accessing the internet).

The problem at the moment is that the speeds I get can fluxuate quite wildly, sometimes I'll get our full 350mbps internet speed but othertimes it'll hover around 50-60mbps (around where the powerline adapter was). I was wondering whether replacing my Super hub 3 with an AX12 router is likely to help improve the connection speed or whether it's unlikely to make much of a difference and it's more likely just a problem with my setup/distance between the Super Hub and my current extender.

I have attached a picture of my extenders connection strength for reference, although that always seems to be good. The worst I have seen is 585mbps on the 5GHz band.

I hope this is the right place to post this, if not please let me know and I'll move it.

Thanks in advance for any help.

Si