I get about the same: 5% for CR increase (solving for efficiency: E = 1-(CR^(K-1)) where K = 1.4).
The valve sizes are already about optimum (1-7/8", 1-1/2", yes?) but opening up the throat is far more delicate than just cutting. It must be done with a piloted ream or stone, and the area just below the seat ID is critical.
The single most important piece of machine work to an old head (aside from the valve job itself) is probably the top relief cut, which should be 15° and just intersect the new seat OD. The seat must be open to the chamber immediately on lift.
Round off the top edge of the exhaust valve where the margin reaches the chamber side. The intake should be left sharp here, just 1/64" radius. Back-cut = yes.
Manifold ports: don't enlarge the exhaust more than the manifolds, and don't blend or radius the transition - leave the edge sharp.
The intake can go up to 1-9/16, but don't go all the way in.
