  We study the renormalization group properties of SU(3) gauge theories with
N_f=8 and 12 nearly-massless fermions, using Monte Carlo Renormalization Group
(MCRG) two-lattice matching techniques to predict bare step-scaling functions
s_b. Traditional MCRG two-lattice matching requires that the renormalization
scheme be optimized for each bare lattice coupling, so that s_b is a composite
of many different discrete beta functions. We propose an improved procedure
that uses the Wilson flow to eliminate the need for this optimization of the RG
blocking transformation. While our 12-flavor results indicate an infrared fixed
point, s_b for N_f=8 is significantly different from zero until strong-coupling
lattice artifacts obstruct two-lattice matching. Although both procedures
produce qualitatively similar bare step-scaling functions, the new s_b obtained
by combining the Wilson flow with MCRG two-lattice matching have the distinct
advantage of corresponding to unique discrete beta functions.
