Performance of scp with OpenSSH - 5.1p1

Hello All,
As the release notes of SSH-4.7 version says that a new MAC algorithm
(UMAC-64 - RFC4418) was introduced with OpenSSH-4.7 which gives much
better performance, I was tempted to check out the enhanced speed
provided with new version. So I downloaded OpenSSH-5.1p1 and build it on
Solaris 10 with Sun Compiler CC.

My test setup:-
1. Two Sunfire 440 with 2 CPU (1281 MHz) and 4GB RAM.
2. Network interface supports 1 Gbit/s (duplex)

I tried transferring 1GB file between Node A and Node B connected using
1GB interface using SCP. Node A can connect to Node B without password
using public key authentication.

With OpenSSH-5.1p1:-
Protocol Time taken rate MB/s
Std. scp 53.7 19.3
scp -c arcfour 40.1 26.3
scp -c blowfish 55.5 18.6
scp -C 123.6 16.3

With OpenSSH-4.5p1:-
Protocol Time taken rate MB/s
Std. scp 59.9 17.9
scp -c arcfour 45 22.3
scp -c blowfish 59.6 17.1
scp -C 131 14.1

I do not see any higher throughput (20%) with the 5.1p1 (with UMAC-64)
than 4.5p1. The above results clearly says it is not increasing the
performance by 20%. Did I something here?.
Also does UMAC-64 have a impact on scp also or my understanding is

Thanks inadvance
Senthil Prabu.S

Senthil Prabu.S