Two LBs.
LB1 runs a 4.8 40, is instinctive, and never misses tackles
LB2 runs a 4.5 40, takes a second or two to process what he's seeing, and is a mediocre tackler.
You will win more games with LB1 than with the much faster LB2. Yes, the lack of speed may be a problem when playing a team...