The only benefit of replacing them the same time is the saving of installation price for the furnace down the road. But you should save much more if you understand JY101's article about HVAC. What I am saying is:
Replace HVAC with "xxxxxxx" brand with the least installation price (it has to be installed RIGHT though). It would also save you $$$ for the future repair work.
Replace HVAC with "xxxxxxx" brand with the least installation price (it has to be installed RIGHT though). It would also save you $$$ for the future repair work.