I would try using 5 or 10 wt less oil. If you drill the pistons out weird like that and don't like it, you are stuck with them that way. If you drop 5 wt oil and it isn't what you are looking for, then you can drop another 5 and see what it does. Or you could use a losi 1/2 weight.
Or do you not have any different oil either? I'm not an engineer so I couldn't tell ya if what you propose would get the same damping as the
6 x 1.4's.