You won't get banned for any hack if no one's around to record you or ban you. However, like the others said, using a value too high or for too long will cause a disconnection. I use 1.5 as my speedhack multiplier and I can last 30 minutes minimum with it on continuously, I'd recommend using the same multiplier.
In case you're wondering, 1.5 isn't enough to permacloak but the buffer between cloaks is less than a quarter of a second so it's pretty much the same thing.