If you have a Venice or San Diego or other RevE core you should be able to run the memory at 200MHz at a 2T command rate, however if you have a winchester or newcastle or other pre-RevE core the memory controller can't handle all four DIMMs running at 200MHz and will run them at 166MHz
Not really, no. Once again yes it's fairly obvious that yes 1T will yield more memory bandwidth than a 2T command rate, but if you were to set up identical systems with one running 1T and one running 2T command rates you wouldn't notice a difference unless you are specifically benching in programs like Sandra or SuperPI so no, there isn't a severe cripple in performance as many like to call it. If you weren't benchmarking, you couldn't distiguish the difference unless of course you were overclocking at which point as I've already said many times RAM is picky with latency and stability therefore the 2T would probably go furtherHe could do that, yes, but in some cases, to get it stable at 200, he would have to run it with a 2T command rate, which severely cripples performance.