1) The 3770K and 3770 both have IMC's (Integrated Memory Controllers) so any overclocking of the RAM is done via the CPU which means that there will be variations in overclocking performance, some 3770's will be able to handle 2800Mhz RAM but I would imagine most cannot. However it's a silicon lottery.
2) For a memory speed as high as 2800Mhz you'll need to manually tweak the memory and appropriate voltages (VCCSA, VCCIO, VDIMM)
3) You can overclock memory without overclocking the CPU in most cases by using the appropriate memory ratio and BLCK value.
4) Read up on Ivy Bridge memory overclocking, make sure you follow the guidlines and stay within safe operating voltages and temps.
Just to note that super high memory speed (E.G 2800Mhz) won't give you much of a performance increase in most applications Vs lower memory speed like 1866Mhz.
In my opinion the small performance advantage is not worth the increased risk or cost.