--comp-noadapt When used in conjunction with --comp-lzo, this option will disable OpenVPN's adaptive compression algorithm. Normally, adaptive compression is enabled with --comp-lzo.
Adaptive compression tries to optimize the case where you have compression enabled, but you are sending predominantly uncompressible (or pre-compressed) packets over the tunnel, such as an FTP or rsync transfer of a large, compressed file. With adaptive compression, OpenVPN will periodically sample the compression process to measure its efficiency. If the data being sent over the tunnel is already compressed, the compression efficiency will be very low, triggering openvpn to disable compression for a period of time until the next re-sample test.
OpenVPN 2.3 Manpage
But I don't know whether it will have an effect on CPU/bandwidth usage. Give it a shot and report, might be interesting