Bigger Headers?

[SubLime440]

Combo:

9:1 / 440 plus .040 over
Heavy Ported / Milled 906 heads w/2.14 / 1.81 valves
Harland Sharp Roller Rockers 1.5 ratio
Hughes HE3038BL Cam (.515 / .536 lift) ( 230 / 238 degrees at .050)
Double Roller Chain
FluidDamper
Edelbrock Performer RPM w/Holley 850 DP
* Mopar Performance 1 5/8" primary tube headers
3700 LB Challenger w/me in it.
Hemi 4 Speed
Suregrip 4.10 Rearend / SS Springs & Pinion Snubber
M/T ET Streets (Weld ProStars) 28X11.50 's on rear

My questions is this.... The headers seem a bit small to me for getting RPM's out of this thing (Headers came w/car) It has good lowend torque (Low 1.8 60ft times at 5900 ft above sea level)
Would it benefit me to go with some bigger pipes say, 1 7/8" or 2" headers... Any thoughts or previous experiences?

Isn't the "Rule Of Thumb" to get headers no smaller than your Exhaust valves... (In this case 1.81 exhaust valve)...

[Darn Dart]

I think a 1 7/8" header and a nice free flow exhaust would really wake up your combo. The small headers you run now might be choking your motor.