It all depends on what your level of computer building and OC goals are. If you are a casual gamer and internet surfer then the Sabertooth will be more than enough power for you and have all the options you need.
The Rampage III Extreme is significantly more in terms of cost and advanced features. If you are a hardcore enthusiast and overclocker then this is the board for you. Especially if you want to use LN2 as your cooling plan.
Yes, the layout is different interms of many features... pci-e slots, layout, power pinouts, bios features, the list goes on and on.
I have a rampage III Extreme OCd to 4.5 Ghz on air ^^ and love all the options it presents me with.
The Rampage Extreme costs on average 365.00 and the Sabertooth should be 200.00, so nearly double almost. If you just wana surf email and play games like WoW then the Sabertooh will do just fine with a good GPU.