I don't believe this will work as intended on machines with Edgy and beyond. From what I understand if you have tcp_moderate_rcvbuf = 1 (which is default) then the receive window is adjusted automatically. Now setting the max values could help but I'm not sure what setting the defalts do when you have tcp_moderate_rcvbuf enabled. Also I believe you will probably want to use net.ipv4.tcp_no_metrics_save = 1 instead of using the route.flush=1.
Here is a website with some tuning tips