But since my case Fractal Design Define R2 comes with two of their 120mm fans, do you think I should play it safe and just get the 800rpm gentle typhoons?

So the Scythe Slip Stream 800 would be a good choice? What about the ticking, does this have that problem? The 19db in your review seems a bit high though...

Is the 1150rpm gentle typhoon more quiet than antec P180 tricool set on Low?

nobody knows?

I want to boost my coming Fractal Design R2's default cooling with a couple of gentle typhoon 120mm's. Is the 1150rpm model more quiet than Antec P180b fan at low setting? Or should I get the 800rpm one?