The problem with being two floors up, the 5GHz will probably simply not have enough range as a general statement. However, you are not getting too bad a signal strength, but you could try moving to channel 52 (see my guide on how to do this). One caveat to this is that some WiFi devices do not work above channel 48, despite the UK regulations allowing much higher channel numbers.
Where the 2.4GHz band is concerned, despite the fact that you have 11 channels to play with, you can only use channels 1, 6 & 11, due to the fact they are the only non-overlapping channels.
In your case, it is difficult to be precise, but I think channel 6 would probably be best, although this can change at different times of the day due to atmospheric conditions. Make sure that in this band, the channel bandwidth is set to 20MHz only (again in my guide), as that is counterproductive in this band. Although currently you are only using 20MHz, but that could be down to your PC's WiFi adapter.
Wired will always be your best option if possible.
The 2.4GHz band has the best range, but it suffers the most from interference, the 5GHz band being twice the wavelength (sorry can't help being a techie) will only travel half the distance, unless the router by design increases its output level. However, even if it did, that would only account for your receive direction, your transmit direction is dependent on the network adapter in your PC & what its output level is. You might guess from this that Wi-Fi problems can be as much to do with the network adapters you use as the router.
The other problem is the location of the router, alas signals from the router rarely travel well to the floor above the router, let alone two floors up, but again your signal strength is not too bad considering, you must be lucky.
Generally, it is best to site the router as close to the middle of the property as possible, on a tabletop with nothing much else around it. Then also make sure that the router & any adapter in your devices are not close to TVs, speakers, cordless phone base stations, large metal objects & fish tanks or other large quantities of water etc.
If your PC is a tower case and the adapter is a card inside the tower, try to ensure the antennae are not buried behind the case (metal once again), if USB, then plugged into a front port or using a short extension cable. Either way, high gain antennae can often help (unless either has internal antennae).
Thanks for explaining that Keith, I appreciate it, and actually understand it! LOL
The router is placed on a shelf, up high on the wall, above the front window. As the main feed is on the front lounge window sill, it limits things. I have a projector on the other side of the room, an AVR with surround speakers, a PS4 and an Apple TV - so there is a lot around it. No phone handset. TVs are upstairs. Loft has more monitors than I have toes LOL! I do manage to stream music and TV in the back garden, which is probably 30 feet away. Although, that's on the phone or ipad. I wouldn't mind spending on a new router, or a cabling system... but with the same low download rate on wired, that makes me question if those options would fix this particular issue.
I am really coming round to the idea that it is the laptop. The PS4 performed much better, so the speed has to be there? And with no better transfer rate, when on wired, that seems weird. Would you agree?
The network adapter is an Intel Dual Band Wireless-AC 3165. That's in a Dell 7000 series, 7th Gen i7. The Dell guy updated all drivers on Tuesday. I have opened up a support ticket with them, to see if they can help in any way. Is the wired port part of this adapter?
Also, is there I anything I can try with the Wifi extender? That's in the loft, and is why you can see EXT2 and EXT5 on the screenshots. I bought that because of the router being stuck where it is, but I actually find the speedtests are better on normal 5GHz, even when in the loft. (I really thought I had covered all bases here, Keith! LOL)
I didn't realise that you had an extender in the loft, this complicates my recommendations. Looking at its specifications it is a repeater, not an extender (despite what it may be marked as), this can have disadvantages, please see my attached guide on the differences between these types of product.
First off, you have a major clash between the router & the repeater with them both using channel 8, but I bet if you move the router to channel 6 the repeater will follow that & use channel 6 as well. This is one of the ways that this type of product can have disadvantages, as it could from time to time cancel out the signal from the router. If it supports its own web interface then you might be able to break this channel following behaviour. The other disadvantage of using the same channel is that any WiFi adapters can suffer delays accessing the wireless medium, thus slowing things down.
Once you have set the router to the new channels I suggested & are connected to the router's networks (SSIDs), temporarily turn the repeater off & get me a new set of screenshots from Acrylic.
Sorry I missed one of your other questions, most laptops & PCs have a separate RJ45 Ethernet port, this is nothing to do with the WiFi adapters that you are using.
I doubt if the problem is related to the laptop itself, that is very high spec with what looks to be a very high spec wifi adapter as well, assuming the drivers have no issues in them of course.
My guides - thanks for your kind comments. They came about after I got fed up keep typing the same sometimes complex things to each individual customer. Now I use the guides plus some macros for the initial reply, but then like your situation as things progress, macros do not hack it!