I have a gateway GW1 which will work fine under normal conditions. If I use a second gateway GW2 and try to send an address list through GW1 using mangle and a routing mark the connection through GW1 will be slow to the point of not working. Doing a speed test, downloads will be markedly slower and uploads wont complete, is there and obvious reason for this? GW1 is unusual in that it is an openvpn client connecting to a remote server through a WAN PPTP tunnel.
Did you disable fastpath/fasttrack? You should.
u da real MVP 
CPU is maxing out at around 10Mbps but ehh that’s fine, running total 3 VPNs anyway