ROMs don't effect real signal strength. There can be variations to how each rom reports signal strength, but the actual signal isn't determined and can't be enhanced by the rom. For example, I've seen one rom constantly bounce around, displaying 1 bar for -90dbm and 3 bars when the dbm was -100+, where another rom was more consistent, but the true signal strength was the same between the two. Probably one just averaged more when determining what to display.
I've battled with low signal strength for the past 2 years on Verizon. Tried every trick in the book, and nothing did a thing. The only thing that helped was getting a network extender.