Upload & Sell: On
Are you sending the files out for printing or doing it yourself?
I agree you will need to uprez unless the landscapes are long-exposure water scenes with little detail. I doubt you will need to uprez to 300 for fine detail viewed at any normal distance (which is probably 2 feet +). More likely 240 will be just fine.
As others have suggested, if you are printing or want to do a test, process your image, uprez, print a full resolution crop to examine sharpening, detail. You might print several 8x10' crops for the uprezzed image, perhaps outputted at 180. 240, 300 and see what you can notice, especially when viewed a couple of feet away. This would work best if you use the same paper for you final prints.