to the OP's actual question, nimh packs weigh a bit more than a nicd pack.
This could be some of the reason you don't feel as much punch. Other than that a pack vs pack comparison between nimh and nicd doesn't work well, without getting long winded....it's not really apples vs. oranges but more like red delicious vs. granny smith. same basic thing just not the same....
If lipo isn't an option stick with nimh, nicds for the most part are gone and for good reason..