If you look in the J&L catalogue it gives the flute length of the stub drills, this is approx the max you should really use them for. Can’t see a 6.1 listed but the 6.0 has flutes of 28mm which is roughly what I said 5xdia (5×6 = 30)
If you do change to a jobber then the normal length Dormer equivalent split point is the A002 series page 35.
Just opened the latest J&L flyer and if you want reasonable spot drills as well the solid carbide Hertel ones are on special
Jason