the comparison between the two mainsails shows the significant difference quite obvious.

In the last act of the AC the German United Internet Team skippered by Jesper Bank reached that event in last minute condition with the old mainhead shape Malcazone used in the last AC while all the top teams were using the bigger headsails. Lacking some power, after racing a few days with the old shape, Jesper Banks team showed up with a sail where additional sailarea was added to the old shape! It seemed that this helped them quite well in gaining performance.

I wonder if you can 'update' the old Taipan 4.9 sails (which have such a little square top that you can heardly call it one) the same way?

Just to comment some other raised questions here:
A wider/larger square top not only increases your light wind performance, but if cut and trimmed correctly, it also helps to open the leech earlier in gusts helping to auto-depower the rig (like surfsails are a good example for).

i think the profile of the godall taipan 4.9 sails are anyhow quite flat in the top, so prolonging the shape could work and one might need some harder battens?

any experience sailmaker around to comment on this?
could be a low-cost option instead of buying a new sail ... :-)