And there is no fan system internal or external that will help - they will only mix the air around - the hot air. In such conditions you NEED something that will exchange the heat in the room for cold - out with the hot and in with the cool. In what I think is your situation there simply is no other way than generating cold air and hopefully also expelling hot air.
Exactly. Having a more hot computer, or a less hot computer is not going to affect the temperature of your office one bit. Therefore increasing the airflow through your computer, will only affect your CPU temps, not those of your office.
That said, if the new Mac Pro idles with a lower power draw than the present one, that may make a difference. Also, you would expect that the new Mac Pro will be able to do the same tasks as the old one far more quickly, thereby producing less heat. So if you are using a new Mac Pro to its full capability for hours on end, no; it will not be cooler. If you are performing a certain amount of computations every day, the Mac Pro will be cooler.
THAT said, if your old Mac Pro is a dual CPU, the new Mac Pro could well be 130W less of a space heater than the old one, assuming you are not using the GPUs.
THAT said, if you ARE using the GPUs, the new system (470W of just GPUs) will likely produce far more heat than the old system.
What you need is a fan blowing the hot air in your office out, possibly into the hallway, or the cool air in the hallway into your office.
Then again, 80˚F, or less than 27˚C, seems quite comfy to me. I would suggest the OP should not visit Australia in the summer
Right here, right now, it is ~21˚C, 70˚F, in the middle of winter, and I'm cold
