my buddie has the screaming eagle slip ons on his low rider and as others have said they dont do much over stock. I had rush on my deluxe and they were great,no tuner needed for just slip -ons.
Have you ever considered the V&H Twin Slash slip-ons? They sound amazing and look great with the Lo. Check out Direct Harley Parts (online); you can't beat their price, they do free shipping and the items get there fast.