Increasing TCP's initial window:
http://tools.ietf.org/html/draft-ietf-tcpm-initcwnd-00

Use at your own risk, but if you were somehow able to download this,
it means that it works for you :)

-Frank.

Index: tcp_input.c
===================================================================
RCS file: /var3/mirrors/cvs/openbsd/cvs/src/sys/netinet/tcp_input.c,v
retrieving revision 1.239
diff -u tcp_input.c
--- tcp_input.c	29 Sep 2010 19:42:11 -0000	1.239
+++ tcp_input.c	28 Nov 2010 09:26:17 -0000
@@ -3138,7 +3138,7 @@
 		}
 	} else if (tcp_do_rfc3390) {
 		/* increase initial window  */
-		tp->snd_cwnd = ulmin(4 * mss, ulmax(2 * mss, 4380));
+		tp->snd_cwnd = 10 * mss;
 	} else
 		tp->snd_cwnd = mss;