Also important is to setup outbound firewall (or other mechanism) so that if the VPN goes down, you don't spew your traffic over the open connection [1].
I don't notice any speed difference from daily usage over the last year. Large file downloads I task my NAS to download outside the VPN.
My purpose is only to prevent the ISP from collecting logs about usage, I don't expect it to have much effect if I'm targeted for surveillance and I'm fine with that. Who knows how ISPs will handle the data (we've seen targeted advertising and content injection in the past) let alone all the agencies with less than stellar security practices.
[0]: https://github.com/thomascannon/scripts/tree/master/vpn [1]: https://github.com/thomascannon/scripts/tree/master/vpn/vpn-...