I’ve got a 500/50 connection. I haven’t fully benchmarked VPN but performance has been fine for what I use it for, even enough to watch HD video if I want. Just testing using my Cell phone at the moment so mileage may vary. I get 40Mbs down without VPN and 30Mbs down with VPN (single file test for both). Upload, I only get about 1.5-2Mbs for both but that is a limitation of the cellular network i’m on.
VPN download speeds will be limited by home upload speed and usually my VPN upload speeds are limited by my local upload speed so its hard to really see the true cost of the overhead of VPN so far.
If I get the chance to try it from a faster, more stable land line connection I’ll try to update this then but it may be some time before I will be able to. I’ve got a buddy with the same internet speeds and provider that would be a good test but his house is being gutted and remodeled so I don’t know when I’ll next get the chance.