M/S winds can safely be doubled to get it in knots. Some EGPWS systems can be used in QFE, check your AFM. The GLEX can be as long as GPS is enabled and operational. Depending on type, lots of systems maybe affected by using QFE. If you choose to use QNH, REMEMBER the controller may give you a QNH setting, but he will always be issuing clearances below transition as QFE heights, you MUST convert using the Jepp table.
GF