GMC Headlite (poor lo-beam brightness!)

[GMC Jim]

GMC uses a 4 headlite system - PAR46 bulb; 5.7" diameter. Original lamps were#4000 lo-beam--37.5/60.0 watts and #4001 hi-beam--37.5 watts.
These trade no's were replaced by H5006 lo-beam--35.0/35.0 watts (very poor lo-beam brightness!!) and #5001 hi-beam--50.0 watts.
By contrast; Chev trucks use 2 - #6014 lamps--60.0/50.0 watts ( a definite improvement on lo-beam brightness! )
In searching for a lamp to replace the low output lo-beams; I find that J.C. Whitneysells a lamp to replace the lo-beam 35.0/35.0 watts with a 60.0/55.0 watt H-4 halogen lamp.
Part # 135ST9319P @ $15.99 each. 100/80 & 130/90 watt H-4's are also available for off-road use.
Plan on replacing the existing (lo-output) lo-beam lamps with the J.C. Whitney subsitute. Would appreciate any comments or furhter information on improving light output on GMC units.