Ram air will only make a difference in HP at high speed like 100+ mph. If the filter isn't completely enclosed from the engine compartment it is definitely sucking hot air and in that case, the stock air box is better.
If the conical filter is completely enclosed, but doesn't have significant air volume surrounding it, it would still be worse. That is to say that you can't just put the filter in a can that has the same inside diameter as the outside diameter of the larger side of the filter.
------------------
351W 89 Mustang GT Convertible