1.4x or 100-400 ?

I am doubting between investing in 100-400L or buy a 1.4 teleconverter (a lot cheaper of course)

would my 70-200 F4 IS with the 1.4x converter be good for outside sports (soccer) ? what about the 2x converter ?

or better invest in 100-400L ?

body is 7D
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EOS 7D _ 400D _ 28-135IS _ 70-200F4IS