In article , "Tony Bryer"
says...
In article , Rob Morley
wrote:
A couple of 5x2 next to each other is pretty much as good as a single
5x4 - they will be more prone to bowing sideways if not bolted
together, but the vertical stiffness will be the same.

Statistically better (2no 5x2 are 1.14 as stiff as a single 5x4 when
calculating to BS5268) because it is highly unlikely that any knots or
other weaknesses in one piece will also be in the other piece at that
point, whilst with a single piece a knot may carry through.

I hadn't considered that, but of course it makes perfect sense.