you could always go up to a Cisco Catalyst 3750G-48TS but that is a lot more $ than your SRW2048 (i think at least like 4x as much) you could also go to a single 6500 although i think you can only use 96 gigabit ports in a single 6500 chassis
if the linksys has everything else you need but you are just worried about backplane between switches why not user etherchannels between the switches to up the bandwidth? that will help with the backplane issue although you will be using up some ports. good rule of thumb is to leave free ports to allow for 25% growth but you would be cutting it close. maybe you could add a 4th switch and that would give you plenty of room