Well that is hard to say, because everyone is different, it maybe significant if you have never used a 12.1 inch laptop before. If the X201 is your only laptop, and you are more comfortable with the 14 or 15 inch form factors, then 14->12 inch change can be significant.
Personally, i find the 13.3 inch WXGA+ on the X301 to be the best... If i don't have a X301, then the T4x0s would be my daily workhorse... i usually take my X200 out when i have lot of stuffs with me in the laptop bag.
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