put the quad in the gamer, put the tripple in the server, a server only needs a single core to function, but since you already have the tripple, might as well
and in desktop appli9cations, there is no improvement after 800mhz
not quite right... theres no improvement 1s you go faster than the cpu rated ram speed.
ie 1066 for core 2, 1333 for i7 9xx and 1600 for 2nd gen i5...
there is quite a jump in performance from 800 to 1066 as long as your latencies are tight you will notice a difference. but only if the cpu supports the faster speeds... everything just runs that little bit smoother. the core 2 going from 667 to 1066 feels like you bumped the cpu by 500mhz and things like float math calcs will get a 15%+ increase in performance. so yeah there is a difference as long as you stick within the cpu's maximums...
if you got an i7 9xx and put in 1333 ram then tested it with 2100+ you are unlikely to see much of a difference other than in benchmarks... all the faster ram really does 1s you go past the cpu's recommended is open up bandwidth so reducing the chance of potential bottlenecks.