I'm hijacking this old thread since I found no other one with answers to my question and this was closest.

I have found really cheap slick tyres, but front tyres only come in 120-sizes. Rear tyre is no problem, can get 150/60 for 73€.

Which of the following sizes would give the best profile, theoretically speaking (since I probably will not tell the difference any way)

120/60
120/70

The tyres are Shinko 008 (http://www.shinkotire.co.kr/)
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MC21, GP-Replica (Daijiro Kato, Telefonica Movistar Team 2001)