[† Flare †]

That depends but slowloris was never meant as a flood attack. If you aren't joking with your statement, I would say a huge number of bots is needed for a GB of power with SlowLoris, but if you are using UDP-Flood, you probably need around 10-100.

[Rekt.]

Slowloris isn't measured in gbit/s. It constantly sends more HTTP headers, but never completes a request.