It is subtle, but you will know it when you feel it. Aluminium frames can be engineered to have more flex, and some steel frames can be overbuilt to a point whe

It is subtle, but you will know it when you feel it. Aluminium frames can be engineered to have more flex, and some steel frames can be overbuilt to a point where the "steel feel" is diminished. So comparing any two random frames may not be sufficient to capture the feel. Also the feeling is subtle enough that the components on your bike can be the larger factor. Tires, crank arms, handlebars, tire pressure, etc.. will all play a factor. Swapping all of your components from one bike to the other would be the best test, but unless your components in aggregate provide a "neutral" feel, it is possible that they could overwhelm the feeling that a different frame will provide.