I assume that the "freqlimits" are for the "transfer" command.
Yes, do look at the spectrum. The choice of f1 and f4, in
addition, needs regard for Gibbs' phenomenon. If f1 is
too close to f2 (in logarithmic space) then you will
get "ringing". I have a very crude rule of thumb to
have f1 <= f2/2 and f4 > f3*2. There is of course no
point in having f3 or f4 > Nyquist frequency.