But that doesn't help if the server isn't multithreaded, no?

Also these days I switched to IPsec. I just get way better performance than with OpenVPN (I am talking about 600 Mbit/s vs 350Mbit/s). But it is quite a beast and you need to have some basic cryptographic knowledge for IPsec.

EDIT: Seems like my first question is only relevant if we are talking about powerful CPUs on both sides. If multicore on client <= single core on server, then this client makes sense.