From what I can find online, most people prefer Sabertooth instead of Z97-A. However, Z97-A supports higher speed RAM, a SATA Express port, and a M.2 Socket 3. So why people prefer Sabertooth instead of Z97-A? Personally, I think the SATA Express port is quite an important feature that would make the board have a longer useful life span, but again, I am a newbie, so what do I know...
Edit: Z97-a also has 5-Way Optimization, which I am not sure Sabertooth supports or not.
high RAM speed does not make a difference (most of the time). And unless you have, or are going to acquire a sata express drive (not many choices) then those features will go to waste. But hear this, if my m5a99fx pro r2.0 had an M.2, I would be using it alot.
personally I would go with the sabertooth because of not-as-flashy brown and black theme versus gold on the Z97-A.
maybe @illuminatiASUS could help in your decision?
The Sabertooth has a 5 year warranty, has a better vrm, looks better and sata express hasn't taken off (m.2 and pcie x4 is a much better solution, no big ugly data cables that remind you of ide).
The ram speed is dependent on the cpu because the memory controller resides there, the motherboard shouldn't have an affect on what clock speed you can run your ram at. For example a system with an i3 2100 is only able to run the ram at 1333Mhz but if I change the cpu to a i5 2500 the ram will be able to run at 1600mhz or more.