Order of mask generator

[Snoopy]

do the fast runs with

?a
?a?a
?a?a?a
?a?a?a?a

until you reach a length of the mask where the ETA seems to long and you want to split

use a single line maskfile with the desired masklenght, now you should be able to use skip and limit option (depending on the speed you have to test some values for limit and skip