It really depends where it's boiling
If you are boiling the the carb, it may do a little as it keeps recirculating the fuel before the carb.
Some tricks though, cool the engine with timing, reroute as much of the line as you can, get some airflow under the air cleaner, phenolic spacer, and even gas formulations boil differently from brand to brand.
That being said, if you do add a return, you want the regulator as close to the carb as it can be, so the fuel dumps just before it gets to the carb. If you do it down by the fender, you arent changing much. EFI systems I try to feed the injectors and dump on return side, but no matter what you do with a carb, at some point, it's just a dead0head hose feeding a needle/seat, shorter the better after a return system