Can anyone tell me if it is any good that actually tried it with ovls/brews and yak?

It's pretty terrible, I've tried it - not to mention void mage is pretty much useless there. Also the only king I noticed a slight difference on was Prime, and it wasn't that big of a difference honestly.

Approximately how fast were your prime kills compared to regular gear?

Well, to be honest I didn't spend much time killing Prime - using both methods (regular gear and void) I didn't have time to actively go out to the safespot and kill Prime - before one of the other two kings spawned. I used a method similar to your 2.5-briding and let deflect curses kill Prime mostly. That way, I don't get over 15 prime kills a trip - I only get to shoot a few crossbow shots at Prime before either of the other two kings spawned (I tried to maximize profits with the two most profitable kings so I didn't really care much about killing Prime). I might try Void and Cannon though, hopefully that will mix things up a bit more. I used Diamond Bolts (e), Leech Ranged and Leech Defence if you were interested what prayers I used - brought an accumulator with me too.

 

Conclusion: It's really not worth the hassle and risk to bring void, there's no real noticeable difference and you get hit alot more in those soft robes :shock: