A 1 in 10 is the standard...I've had a number of 243s and the 1 in 10 prevails.  I would not worry too  much at all.  My Tikka T3 Hunter puts 90gr nosler ABs in a nickle sized group easily.  Also, I'm not at all interested in shooting bullets lighter than 90gr...preferrably 100gr partitions.  I've taken deer and exotic sheep/goats with 90, 95 and 100gr bullets and 1 in 10 twists and had NO problems with accuracy.