I'm curious as to what percentage each hit increases damage.

I've been wondering about this too.

If it's significant I have high hopes for a furious ripper!

I have one its beast. In vats it seems like damage increases by 10% per tick but that's a guess.

I'm wondering what percentage it caps out at. If it just keeps getting stronger and stronger indefinitely, a Furious Ripper could destroy a Mirelurk Queen in seconds.

When I cap out damage its 330, with overdrive and all the other drugs I can kill a mythic deathclaw in 2 ticks from the ripper. I pop ultrajet and kill everyone before the chunks land. And those 10.6x crits mmmmm. Pretty much nothing stands a chance.