LFB has higher tensile (65-70kpsi) and shear strength so it is stronger than say 38%/Fillet Pro (40-50k psi tensile). As John points out, silver is a bit trickier to build fillets with - though I suspect he's referring to 56% instead of 38%. 38% builds fillets pretty nicely but heat control is critical. LFB is more forgiving in my experience. For me, 56% for building a fillet is just silly. I"d have silver all over the place before I built any kind of meaningful fillet!

Practically, the silver fillets should be somewhat bigger than the brass ones because of the lower strength. I think most of us make (or maybe historically) our brass ones bigger than necessary for strength anyway. There's a formula for calculating how much overlap is required for a lap joint (lugs) but I haven't seen one for filleted T joints.