No, both "guest networks" are kept separate, I'm aware I would need a managed switch for that (they also in different subnets, which I don't know if that matters but I did just in case).
edit: by 'separate' I mean that in the vlan's there's no shared ports anywhere, I did both on router and dumb ap as it's posted on the original thread (i.e., option ports '2 0t' instead of options ports '2t 0t' with a '2t' on the 'lan' part of the network).
Ok... good. Yeah, I don't know why you're having this issue.
Ok. but thanks for the help. Good to know that's it's at least not something obvious. So what's the difference here between the 'guest' and 'lan' networks? Couldn't in theory I make an identical copy of 'lan' so that everything's the same, and see if I still have the problem?
could be worth a shot -- can't be truly identical, of course, but you can make it as close as possible.
Another thing you can do is to force the link speed if the option is present (I think you might need to install an additional package for swconfig). By disabling auto-negotiation, that could possibly help But still, the numbers you get are not seeming to be limited directly by the standard port speeds (typically best case real-world bandwidth is ~94% rated link speed in full duplex, half duplex will be less (maybe reaching ~60-70%).
I ordered an unmanaged gigabit switch... if that also fails then I'll keep down the rabbit hole 
Edit: Actually, I just tested it with the unmanaged gigabit switch I had (I just plugged it in the 'guest' lan port, and connected to the unmanaged gigabit switch ports), and the internet speed is up to 140Mbps. So, the problem is some sort of hardare/software compatibility problem with old 10/100 switches (or perhaps my two specific hardware, Archer C7v5 and WNDR3700v1 with the 10/100 switch hardware/software). If someone else is having this problem, just spend $20 for a new gigabit switch and save a whole day of tinkering 
Glad to hear the problem is solved!
This topic was automatically closed 10 days after the last reply. New replies are no longer allowed.