Welcome to Tom's Forum!
Not exactly, it's a Multiplier of the FSB or BCLK equal DRAM Frequency, but the Frequency internally to the RAM is 1/2 relative to its expressed frequency (DDR = Double Data Rate). DDRx strobes twice per cycle on both the top and bottom of it's sine wave.
ANS (1): Assuming you're referring to the CAS Latency then yes the performance of RAM alone is a function of both Frequency and CAS, and both are important; calculated as: CAS / Frequency MHz * 1000 = X ns. However, rarely expressed as an integer (whole numbers).
ANS (2): Depends on the Frequency and CAS Timings of the 4GB and 8GB density kits. Often, the loss from using 2xDIMM per channel is compensated or exceeded from the gains in Higher Frequency and Lower CAS of the 4GB density kits.