On the m20 we made a 1m longer pole than std. Was always better. Yachts have the same issue, longer pole faster and deeper is the result.

To deal with lee helm you have several options. Most effective is to move boards forward, a 25cm longer pole is usually offset by 5-7cm forward with the board. not so easy to do but most F16 designs I have seen are on the aft side of fast from my observations. Particularly the taipan which is what Wouter is basing his observations on.

You could fit higher aspect boards in the original cases, this will have a similar effect.