I genuinely can't comment with certainty about the WRC engine configuration as I don't know what their development issues were. Development it usually necessary due to issues found during testing that were not forseen during the design stages. Whilst many would wrongly assume that increasing rod length was for a power gain, I would suggest it was more a function of reducing bore deformation due to the higher compression ratios, 102 ron fuel and high cylinder pressures used to optimise the engines restricted power output.

I would speculate that the reason they started to use long rods was not for reasons of best power output (because as Ive allready said a lower rod ratio gives best bottom end torque) but because it was a means to an ends for making the engine more reliable. This is not something that applies to the average cosworth owner because bore distortion is'nt actually an issue for what Id deem a conventional cosworth spec engine running on pump fuel.