ATX case full or mid

I am building my system have all the components, but havent decided on my case. I have a old gateway 2000 with a full tower atx and a 165w power supply. My new case is a mid tower with a 300w power supply. I am thinking of switching all of the old hardware (165w p.s. 430fx and pentium 1, cd, and floppy) to the mid tower. I am then going to move the 300w power and 80mm fan to the old gateway full tower. I plan to add all my new components to the bigger tower so I can have room above my mobo and have a better flow of air so my XP-2000 gets plenty of cooling. ANY SUGGESTIONS , AND AM I ON THE RIGHT FRAME OF THINKING? THANKS ANY IMPUT WOULD BE APPRECIATED.