Britannia flew a loaded 763 direct Newcastle to Orlando (Sanford) every week through the Summer last year (replaced by MON/TCX A330s this Summer).
The runway there is 2,329m (7,641ft) in length. I don't see the EDI runway length being an issue therefore.
The most important runway length though I uunderstand (for performance limitations and calculating Performance-Limited TOW) is ASDA (Accelerate-Stop Distance Available).