@Byrd1 

Hi,

How old the cables are is not so important for the performance of the Powerline adapters. 

Key factors affecting the data throughput speed are high-frequency electrical noise and electrical impedance, both of which are introduced by the various electric appliances one has connected all through the house. 
Furthermore, do you know if the mains sockets in your house are connected via three-wire cable? (or in other words, does the cabling inside the wall have a separate Ground wire?)

As far as I know, one reason for the AV1300 Powerline adapters achieving their higher speeds is that they use a technology called "2×2 MIMO", which however requires the use of the Ground wire in addition to the other two wires.

  @woozle 

Thanks Woozie. I don't know if there's a ground wire in the walls, but I doubt it. I guess the only way is to take a socket out and have a look. I don't think there's much else I can do, apart from the TV and fridge, there's not much else plugged in anywhere besides the PC.

Thanks for your help!

  @Byrd1 

Hey Nick,

Congratulations on your new house! It's great that you're using an AV600 pass-through kit for wired internet upstairs. Based on your current speed of around 140Mbps, which aligns with TP-Link's estimates, it seems like you're getting a decent connection. Upgrading to AV1300 Powerlines might potentially result in a noticeable increase in speed, but it depends on various factors, such as the quality of the existing wires in the walls. While the AV1300s could theoretically provide speeds of up to 1300Mbps, it's difficult to predict the exact increase you would experience in practice. It's worth considering the possibility that the cables in the wall may limit the speed to some extent. It might be helpful to consult with TP-Link or a technician for more accurate guidance based on your specific setup.

Best of luck with your upgrade, and I hope you enjoy a faster Worth and more reliable internet connection!

  @tomcruse412 Thanks!

My theory is that if I get 140Mbs using the AV600 (which is about 25% of the theoretical maximum), then I should get about 300Mbs if I swap to the AV1300 (again about 25% of the maximum).

But I'm not sure if it will work like that in real life. As you say, I guess there's a lot of factors. I've also seen that there's an AV1200 version where the repeater module (I made up that name, dunno what it's called; I meant the bit that doesn't connect to the router) has wifi built in. That would be pretty helpful, but there soooo expensive!

Thanks again.