When sizing a walk in you must first size and select the evaporator to handle heat absorbed from product,transmission of heat from outside refrigerated space,air infiltration through door use and other misc loads such as lighting,machinery in room,req'd air changes and people working in room.
I haven't done a load calc on your setup but if the room needs 30,000 Btu then it needs 30,000 Btu ! Putting in req'd evaps and shortchanging the cond. units is stupid. Your system will suffer in the hotter ambients, mind you it may run fine the rest of the year but what's the point if it dies on the hottest day of summer and its fully loaded - if it can happen it will happen!
Quote two appears to be a more evenly matched system providing it has the req'd evap capacity. In my experience I have found it better to slightly oversize cond. unit. The result is you usually have to cycle or speed control one condensor fan to balance system during low ambients but customer ends up with a system that works 365 days per year. If evap load is 30,000 Btu personally I'd like to see condensing units rated at approx 31,000 to 34,000 Btu at max ambient for your area, this also allows for dirt that WILL collect on evaporator and condenser surfaces and other wear.