Couple of things.
Firstly, I'm not sure how much you can effect graphics card temperatures with case fans in a Prodigy. Having a larger fan at the front should, in theory, spread some cooler air in that direction, but it's a pretty small gap along the side of the case so it's not going to make a world of difference. I have a GTX660 in a Prodigy and while it's not the hottest/power hungry card, I can't make any difference to temps by installing fans in the roof or in the front.
The main disadvantage of having a single 120mm fan at the front is that it is probably just blowing against the HDD cages and not really doing a lot to help the flow through the case. For that reason, a 200/230 can make quite a nice difference, as can a 140mm as the mounting points for this push it above the HDD cages (assuming you have only the bottom cage installed).
A 230mm fan sadly does not have 32% more area than a 200mm fan. No fan is actually as big as it says it is. In the case of 120/140mm, it's a the square box surround that is 120*120*(depth - often 25mm) or 140*140*(depth).
When you get bigger, the mounting points aren't quite as standardised, and neither are the sizes.
A Bitfenix Spectre Pro 230mm fan is
around 180mm in diameter
A Bitfenix Spectre Pro 200mm fan is
around 180mm in diameter
I understand the 230mm is slightly bigger, but based on those drawings it's hard to see, it's that small. The 230mm fan is 5mm deeper though, meaning they can use deeper blades, effectively a greater angle of attack for better airflow. There isn't going to be a vast difference in performance though.
What I would say is that if you want to boost the system airflow as a whole, adding a quality 140mm to the back and any of the three larger options to the front is likely to give you a decent improvement. There are a couple of caveats to that though - If you are solely interested in proving graphics card temperatures, neither of these is going to help much. Also, having a 200/230mm fan at the front running at full speed is incredibly loud. I use a mesh front Prodigy with a 200mm fan, and it is by far the single loudest component at 100% speed, probably because it's nearest to me and there is nothing to muffle the noise.