2.4ghz signals penetrate walls and have longer distance than 5.0ghz. Running mixed can cause some problems with some routers so make sure your firmware is up to date on the router.

Range extenders will cause a loss in throughput and LAG will increase if your a gamer. If you fine it troublesome give the powerline adapters a try. The only thing that seams to impact them is noise on the line from motors/compressors and sometime a bad power pack for a phone.