RVSM requires that at sea level there is a MAX 25 feet between capt and 1st officers altimeters. MAX 75 feet difference between capt or f/o altimeters and airfield elevation, at all elevations.
At 5.000 feet field elevation there is a MAX 35 feet diff, and if the field is 10.000, there is a MAX 40 feet difference.
Inflight the max difference between capt and f/o is 200 feet.
From Boeing B-757 Ops Manual, limitations chapter.