Various layer heights, extrusion width varies with layer height, but "perimeters extrusion width" is always the same as my nozzle diameter, 0.35mm.

perimeter layer heights

; generated by Slic3r 0.9.11-dev on 2013-07-10 at 20:50:53

; layer_height = 0.35
; perimeters = 2
; top_solid_layers = 2
; bottom_solid_layers = 2
; fill_density = 0.3
; perimeter_speed = 80
; infill_speed = 100
; travel_speed = 300
; nozzle_diameter = 0.35
; filament_diameter = 1.75
; extrusion_multiplier = 0.9
; perimeters extrusion width = 0.35mm
; infill extrusion width = 0.37mm
; solid infill extrusion width = 0.37mm
; top infill extrusion width = 0.37mm
; first layer extrusion width = 0.88mm


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; generated by Slic3r 0.9.11-dev on 2013-07-10 at 20:51:37

; layer_height = 0.3
; perimeters = 2
; top_solid_layers = 2
; bottom_solid_layers = 2
; fill_density = 0.3
; perimeter_speed = 80
; infill_speed = 100
; travel_speed = 300
; nozzle_diameter = 0.35
; filament_diameter = 1.75
; extrusion_multiplier = 0.9
; perimeters extrusion width = 0.35mm
; infill extrusion width = 0.37mm
; solid infill extrusion width = 0.37mm
; top infill extrusion width = 0.37mm
; first layer extrusion width = 0.75mm


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; generated by Slic3r 0.9.11-dev on 2013-07-10 at 20:52:10

; layer_height = 0.25
; perimeters = 2
; top_solid_layers = 2
; bottom_solid_layers = 2
; fill_density = 0.3
; perimeter_speed = 80
; infill_speed = 100
; travel_speed = 300
; nozzle_diameter = 0.35
; filament_diameter = 1.75
; extrusion_multiplier = 0.9
; perimeters extrusion width = 0.35mm
; infill extrusion width = 0.39mm
; solid infill extrusion width = 0.39mm
; top infill extrusion width = 0.39mm
; first layer extrusion width = 0.62mm


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; generated by Slic3r 0.9.11-dev on 2013-07-10 at 20:52:39

; layer_height = 0.15
; perimeters = 2
; top_solid_layers = 2
; bottom_solid_layers = 2
; fill_density = 0.3
; perimeter_speed = 80
; infill_speed = 100
; travel_speed = 300
; nozzle_diameter = 0.35
; filament_diameter = 1.75
; extrusion_multiplier = 0.9
; perimeters extrusion width = 0.35mm
; infill extrusion width = 0.67mm
; solid infill extrusion width = 0.59mm
; top infill extrusion width = 0.59mm
; first layer extrusion width = 0.62mm