I think noobermensch is correct here. The American skill 7 tank tech team does tank research slightly faster than Christie at skill 5 (with full matches). Likewise the soviet infantry tech team is worse at infantry research than Mauser, who is skill 9 with three matching fields.
generally speaking, its more important to know what kind of tech teams you have at your disposal, because its better to research the relevant technologies in the correct time with the correct tech team. So in a sense try to avoid having your best tech team being "occupied" in another research when you have to do a critical tech.