[alice]

If it whines as bad as you say it is, the whine is not going to get any better. The set up is probably the issue. I've set up rear gears all my life and gear noise is most always caused by improper pinion depth. The poly bushings amplify the noise for sure but is not the primary cause. I have 5:36 gears with 30.5" tall tires in my Camaro and though some gear noise is expected as you go up in numerical ratios, even with ratios as high as mine, I only have a small, acceptable amount. For sure, the poly bushings had to go because I hate noise.

The best lube for reduced noise levels is the Lucas brand. That is my experience. Your 3.91/4.10 gears should make little to no noise especially if you go back to stock bushings. Your noise will not wear in or go away until the gears are properly adjusted. Won't hurt anything but certainly is aggravating. As far as noticeable increase in acceleration, it will be a small amount. Usually, to notice a real seat of the pants improvement, you need to increase ratios in increments of .3-.4. But you should notice a difference. Have fun!