  For a mixed stochastic differential equation involving standard Brownian
motion and an almost surely H\"older continuous process $Z$ with H\"older
exponent $\gamma>1/2$, we establish a new result on its unique solvability. We
also establish an estimate for difference of solutions to such equations with
different processes $Z$ and deduce a corresponding limit theorem. As a
by-product, we obtain a result on existence of moments of a solution to a mixed
equation under an assumption that $Z$ has certain exponential moments.
