New Rudder verses Old Rudder

I am new member and have really enjoyed your post. I am very interested in Yacht Desing but only from a Hobby point of view. I read all I can but after looking at some of the post is became obvious I have not read nearly enough.

I sail and race Hunter 28.5 and needed to replace my Rudder. The company I am buying the rudder has said after looking at my old Foss Foam Rudder that with the new design I should expect quite a nice performace gain over the older design. The older design from a side view had both the leading edge and trainling edge sloping to each other. With the bottom of the rudder being maybe half the fore and aft measurment as the top of the rudder. My new rudder will have the same surface area as the old but will have a straight leading and trailing edge with a slight curve aft at the bottom ofthe rudder. I also think we are going with a 12% foil verses around a 16% of the old design. I hope I have explaned it close enough but will a rudder of a good design have a overwhelming effect over a rudder of a poor design?/

Thanks Cliff Ruckstuhl