Cashflow: Pay Mortgage at Accelerated Rate or Save to Buy More?

[Naji Saba]

Seeking advice!  Similar topics to this question have been posted but seem to be more than 2 years old and have nuances/details not related to my situation. 

Purchased an investment property for $330k (Typical 20% down - rate is 5.5%! YUCK) which consistently cashflows more than DOUBLE the PITI. I have been habitually making extra-large payments to the mortgage, typically 40-50% extra on top, straight to the principle. Occurred to me that maybe I should just pay the minimum required (PITI) and save up the extra cash to buy another property...

Opinions on best strategy?