Your router is specialized hardware and software so it's pointless to compare it to your desktop PC clock speeds. If you are concerned the router is getting overwhelmed you can view the status page for CPU usage.
Most likely you will be limited by the throughput of the VPN provider or the destination site/service in almost every case. I'm not sure there's any provider that could guarantee a reliable 250/250 VPN connection. Such a service would be very expensive if it exists.
I have 200/200 What I found out recently that all the servers are not the same and once I started to connect to those listed with higher speed users I started to see big difference :
So when the supplier (AirVPN) says that 30/30 is the max that specific router can handle, they're lying?
I would want to know where they got that number. Is it based on something ASUS published? Is it based on in-house testing at AirVPN? If it's based on their own testing what were the conditions of the test?
They may be right but without context it's a bit hard to trust. You yourself said you got 100Mbps which would make them wrong. I have found that ISPs (and by extension any network provider) are all too ready to blame slow speeds on someone else. It's an easy way out and they don't have to do anything.
The problem is that I have no way of proving them wrong. I used to work with networks, but not at that level, and I don't have the equipment. That's why I was hoping someone here knew something. As is I just asked to return the router as I have a perfectly good router, from the ISP, but that one can't do VPN. But when I can't get VPN over 30Mbps, or no-one seems to know anything, I just can't justify using that much money on something that might not work. Sure, it has Tri-band and is probably better, but I don't need WI-Fi for anything other than my IPad, the rest is connected directly to the router.