When I visited the Ludington pumped storage facility 25 years ago they claimed the efficiency was 70%. If Wikipedia can be believed it's been upped by 5% since then with new turbines. Of course if it's on the 'net it must be true.
The facility was supposed to be used in conjunction with the planned nuclear Midland Power plant that was never completed. With a nuke plant supplying the electricity the expected 30% loss was considered acceptable and would maximize the use of the plant. The only problem was it ran Consumers Power out of money. Construction problems delayed completion and 3 Mile Island made nuclear energy the halitosis of power generation. Midland was finally finished but it's not nuclear.
-Tom