В сообщении от Вторник 21 февраля 2012 18:31:24 вы написали:

quoted

But maximum speed in 3.1.10 kernel (without this sysctl settings) still
a bit more than in 3.2.7 - 11 MB/s instead of 10.3 MB/s.

--2012-02-21 18:56:36--  ftp://ftp3.de.freebsd.org/pub/FreeBSD/ISO-IMAGES-i386/8.2/FreeBSD-8.2-RELEASE-i386-dvd1.iso.xz
100%[======================================>] 2 066 424 512 11,0M/s   in 3m 30s
2012-02-21 19:13:55 (9,39 MB/s) - «/dev/null» saved [2066424512]

Thats one measure, you'll have to make a lot of different measures to
make this significant, preferably in a lab to rule out different
external network conditions.

So, I did a couple of download tests from ftp3.de.freebsd.org with kernel 3.1.10.

Here traffic plot for net.ipv4.tcp_rmem="4096 87380 897664":
http://img848.imageshack.us/img848/2425/net897664.png

Here plot for net.ipv4.tcp_rmem="4096 87380 4127616":
http://img14.imageshack.us/img14/311/net4127616.png

And comparison of both plots:
http://img684.imageshack.us/img684/7163/netoh.png

The main notable difference is that with 4127616 there is
never stright line (when wget shows 11 M/s ) as with  897664.
Speed with 4127616 is close to 11 M/s but never constant.
I was able to reproduce this at least 3 times.