scp performance

[comfooc <comfooc%gmail.com@localhost>]

Hi,
few weeks ago i made some test using scp.
Systems were out of the box.
Machine 1 : OpenBSD; P3 500Mhz; 192Mram; 10Mbps;
Machine 2 : tripleboot :OpenBSD, Linux, NetBSD; P3 750Mhz, 512Mram, 100Mbps;

Transfers were:
Machine 1 <=average 800KBps=> Machine 2 : Linux
Machine 1 <=average 550KBps=> Machine 2 : NetBSD
Machine 1 <=average 950KBps=> Machine 2 : OpenBSD

What might caused that low transfer? How to improve it?
Cheers...