I have that Shorokh kit on my 350mm barrel at .30cal. It's still very noisy for my backyard. I am detuning mine to lessen some noise. I changed my regulator from factory stock of 130 to 85 and now I took out the factory jet and installed a jet size of 1.3mm. I'm using the factory original power puck that is 5-6mm in size. My chrono reads around 615 FPS and its a lot quieter now. I will probably try 70-75 and hope I receive NO magazine lockup.
I got the 25 cal, out of the box it chronograph at 890fps with JSB 26gr. I would definitely say on the loud side for backyard plinking too.. I will keep mine at factory settings because I am pretty happy with its accuracy out of the box... I was consistently hitting a 4" gong at 100yds while standing unsupported. The balance of the Leshiy2 with the 350mm Shorokh kit and 3.5L bottle is PERFECT!