To the OP,
I had a local gear guy do them. Specs are specs, but in the end, the pattern obtained will dicatate noise or the lack of. A seasoned gear installer will ensure a quiet set of gears. Assuming the setup is within specs, fine-tuning the pattern will make the difference. Mine are Yukon 4.56's installed with original carrier and pinion bearings, no noise at all.
As for rpms, it is important to compare apples to apples. So lets start with stock assuming a couple things, V-8 = 545RFE so a 0.67 final overdrive ratio and 3.73-1 axle gears. Stock tires are 235/65R17 tires so an even 29" diameter according to most tire manufactures.
29" tire, 3.73 gears, 0.67 OD, 70mph = 2027 rpms.
31.7" tire (265/70R17), 3.73 gears, 0.67 OD, 70mph = 1854 rpms
33" tire (285/70r17), 3.73 gears, 0.67 OD, 70mph = 1781 rpms
33" tire, 4.56 gears, 0.67 OD, 70mph = 2178 rpms (151 rpms more than stock)
The WJs take their speed signal from the tone ring on the rear axle shaft. Gear ratio has no effect to the speedometer, only the tachometer. So as we go from a 29" tall tire (719 revolutions per mile on tone ring), to a 31.7" tall tire (657 revs/mile on tone ring) our speedometers read 8.6% slower than actual speed. So if you are showing 70 mph on your speedometer (assuming no electronic reprograming) you are actually traveling 76 mph. Plugging in an actual speed for 31.7" tire, 3.73 gears, 0.67 OD and 76 mph = 2013 rpms. This will continue to hold true for a 33" tall tire (630revs/mile for tone ring) equalling a 12.3% difference in true speed. So if you speedo shows 70 mph with the 285/70r17 tires, you are actually traveling 78.6 mph. Hope this all helps.
For what it is worth, I love my 4.56's and find the taller and higher the jeep goes, my sustained freeway speed goes down, but only because of my head. The fuel mileage drops because of rolling resistance and increased wind resisitance so I find myself slowing down a little to accomodate it. If I didn't care, the jeep's V8 wouldn't either. It'll hold whatever speed I want. As I mentioned earlier, the biggest difference has been towing my 19-foot Heartland MPG camper that weighs about 3200lbs wet.
'78 Cherokee Chief: 360/TH400/NOS QT, '04 Grand Cherokee: 4.7/545RFE/242HD w/SYE, JK Rubi front axle, 4.56 gears, Protofab rear bumper/tire carrier