Splitting the progression slope curve in 3 pieces didn't help much with precision, I will try later today with a radial array of 90 pieces and see if it makes a difference then. Flow tool in V5 behaved more or less the same as in V4, I didn't notice particularly better tolerances. Helix should have 32.5mm in diameter, but when selecting it dimension was between 32.46 and 32.4999, I guess small roundings per each interpolation point add up at least in this particular case.