I use Verizon Fios and get a steady 12.5 on every device. Though once I hit about 3-4 devices doing things all at once that are bandwidth intensive, the rate starts to drop. Obviously the PS3 and PS4 are doing gaming activities, but I never use both at once. I have my laptop, my wife has a tablet and her phone, I have my phone, plus the TV. If she is streaming a video on her tablet and I'm gaming, regardless of system, you notice a bit of drop but nothing really noteworthy. It's when my laptop starts doing things as well that it'll get start really affecting performance. When the TV is doing some streaming, that can really affect performance on everything else because it is so incredibly inefficient or something.
Thankfully with Verizon Fios, other people doing stuff in my area don't affect my connection unlike Comcast. Peak times I always get the same speeds which allows me to use a lower tier than with Comcast I need a higher tier. It's a lot better during off-peak hours, but at peak times I'm getting the same as I would Verizon. I've found for my gaming purposes right now, the ~12.5 is more than sufficient. That might change when I get ESO.