I manage a fleet of lenovo machines, from back in the days of T20's to now the main work tool of trade is the T420. We have a handful of X220.
We also used the X300 seiries which were fantastic devices, battery was woeful but most loved it. We assumed the X1 would continue this theme, I bought one to replace my three year old X300 and have to say its awful. Wieghs a tonne, its thicker than the T420 (much thicker and heavier than the X300) and is so slow for a new machine. Keyboard is not as tactile, screen is shiny/reflective and wobbles as you type. No VGA output is a problem in the business world, yes you can get a dongle but it is crazy not to have this built in. No CD rom where as the X300 had that too and still thinner.
It also has a flappy plastic cover over the USB & headphone sockets??? You need long finger nails to prise it open and then to get it to fit back is really awkward. Might just as well rip it off.
Speed wise there is not difference in real world use. Battery is just as bad.
I would not recommend buying one, get a X301 if you can or a second hand one.