In the application for which I use the VPN, performance isn't much of an issue--I'm using it to admin stuff inside my LAN, from outside my LAN. As long as I can get a few tens of kb/sec, it's plenty. If you wanting to use the VPN outbound from your LAN, for example to hide your torrent traffic, or to circumvent GeoIP-based blocking, that's a different scenario. I'd still tend to think that should be done on the router, but it's not a use case I've had a need for, so I haven't thought much about it.