No such thing as there are too many variables and combinations of rifle, stock, mounts, scope, pellet, calibre, etc.
My fettled TX200 MK1 could punch one whole groups at 35 yrds but used to open up at long range.
My Theoben Rapid 17 FT punched tighter groups than a mates Pro Target.
My XL1 punched the tightest groups Ive ever seen and very consitantly so for me the XL1 with fixed 35x Leopold and Crossman Premiers was the most accurate combo Ive shot.