The processor speed of 551 actually is 600 Mhz.
GSM arena actually misled me. (sob sob,I feel like n00b)
What I found out with help of some tools and some fiddling.
I used Set CPU from the XDA developers site to check and used Droid explorer to confirm it.
the 551 has actually a ARM 6 rev 5 with only 600 Mhz
The cheaper galaxy 3 has 667Mhz.
Use Droid explorer to Access.
You will find all the relevant info here.
Note to access using droid explorer Phone should be rooted and have busybox installed.
Z4root does both.Rooting voids the warranty.
Ironically the samsung Box and website have no information of the processor
Shame on you samsung for withholding this important piece of information.