I only use OpenVPN regularly. My internet connection is either 100Mbit or 1Gb both up and down, but depending on where I am the actual external bandwidth varies - mostly it's around 50Mbit end-to-end, subjectively. If I send data at max speed through the network then I observe that OpenVPN may use quite a bit of CPU (maybe up to around 40% of one core (i7-7500U), but it doesn't limit the transfer speed I get compared to when I do a direct transfer without VPN (interestingly, on long latency lines (when I go OpenVPN from Japan to Europe) I often get better and more consistent performance when going through OpenVPN (configured to use UDP).