Does your comparison take into consideration the S/D resort fee of $15/day? For a 10 night stay, that could add $150 to your total stay.
Also, have you added the cost to either park your car if you're driving (or renting a car) &/or the cost for airport transportation which won't be complimentary at S/D?
Reason being, we're (tenatively) doing a split POP/Dolphin stay for 10 days. When I add the resort fee & airport transportation to my discounted Dolphin room rate, Dolphin for 3 days is still almost as much for us as POP for 7 days. I don't know what your discount was, but if you are able to book Dolphin for only $600 more than POP for 10 days, including those extras, hand down I wouldn't hestitate to book Dolphin!
You can always book POP the next trip you don't have a discount. Unless you've got your heart set on getting a dining plan, staying at a value vs. a deluxe resort is what it boils down to for only $60/more per day.
We're looking forward to our split stay, having not stayed at either resort, but we have stayed at Swan so I know I'm looking forward to the end of our trip stay feeling a little pampering over at Dolphin with the heavenly beds, grotto pool, dining options beyond the food court, Epcot right next door, DHS a boat ride away, the location is fabulous! Other than a monorail deluxe resort I don't think you can beat the location if you're relying on WDW transportation to go to the parks.
Good luck deciding!