Buy and hold SFR's in Houston-Question on lease ranges

I realize Houston is a huge market, but what are some % of value ranges that fellow investors are seeing for rental properties? I'm trying not to go by a hard and fast 1% or 2% rule as it really depends on running the numbers diligently and seeing if it works. But is there a ballpark range I can go by? Also, if you purchase a home at below market value, do you figure the rent ranges based on the purchase price or the true market or ARV? Thanks.