Read it again. The A310 and 777 are not three-engine aircraft -- they are two-engine aircraft and thousands of them cross the Atlantic every day. Are you worried about asymmetrical thrust on one of those after losing an engine?
Two-engine aircraft are designed to deal with the loss of any engine without danger. My question is whether a four-engine aircraft that is missing one will still have the safety margin of being able to withstand the loss of any other engine without danger. And asymmetrical thrust is my concern; on a 777, the engines are all located near the central axis, so the moment generated by assemmetrical thrust would be somewhat limitted. I would expect that on four-engine aircraft, the moment generated by using two same-side engines would be greater. Cutting back power on the outside engine could reduce this moment, but I don't know how much spare thrust is available. To be sure, I wouldn't expect the plane to fall out of the sky with two engines (since maintaining flight should require a lot less thrust than taking off) but I would think controllability would suffer greatly.