FWIW, yesterday I tried an experiment. I have OpenVPN configured between my notebook computer and firewall. With my notebook connected to my local network, I ran speedtest.net and verified it was going through the VPN. I could not notice any difference between using the VPN or not. Any difference was within the normal variation for speedtest.net. I run pfSense on a HP 5150, with 4 GB of memory.
Incidentally, I have a 60/10 package from Rogers and generally get mid 70s down and 11 up, but yesterday I was getting almost 100 Mb down.
I haven't lost my mind. It's around here...somewhere...