Sunbeams = nickel
FatBeams = stainless steel
Both are round core, so tension is similar...Fat Beams maybe a hair tighter.
FatBeams will be brighter sounding and rougher feeling since they are stainless steel. They will have less midrange than Sunbeams.
Both are great, just depends on what you're looking for.
You might consider Dragon Skins, which are similar to FatBeams/HiBeams but are coated. So they should basically sound like FatBeams but less bright and smoother feeling. But I don't know that for sure....yet. I haven't used them. You can get any of them here, and even build custom sets: https://bassstringsonline.3dcartstor...ings_c_16.html