A good bow will always out-perform a lesser bow regardless of weight or timber.
If the yew bow took some compression damage, has string follow, doesn't have an efficient tiller shape etc, a well made elm bow of the same weight will kick it's ass every time.
Interesting that you ended up so low in weight with the MR replica. My recent replica of MR80A0907 (one of the smallest bows found) was 100 @ 30", and that was using very poor quality English yew. Your elm replica was much lower than the original as well, as Jeremy's reproduction was 141lb. Are you starting with the original dimensions and reducing as you tiller, or are the final, finished bows the same size as the originals?