The cascade option is intriguing... but by time you purchase and plumb in the cascade cylinders and add additional filtration (another $3-4k), you may as well just buy a larger compressor.To cascade gas I guess it would depend on the duty cycle of the unit. Say to do a 5 bottle, 2000 cf system to 3000 psi would take 37.5 hrs to fill. To get the bank up to the normal 4500 psi, being conservative would take another 18.hr for a total of 56.25hr.
For fun - assuming I could modify the intake to get a mixing stick in there, is this little compressor rated for up to 40% oxygen?