frequency plans with BBH are to tight where traffic is high. For your case, your reuse partern is 50/4 about 12 not to good in GSM because the reference value is around 15. If you separate BCCH and TCH bands (mandoratory to avoid HO Fail)your TCH reuse partern would be less than 12 still not to good, because you will need at least 15 frequencies for your BCCH.for me it is better to implement SFH; you should just be careful with your design.