A while back I did a comparison of the two rear ratios for given speeds. I used an online calculator that asked for final drive, tranny ratios and tire diameter (I used 18" stock dia of 33.17")
1st gear @ 20mph 3.73=3002rpm/4.30=3461rpm
2nd gear @ 30mph 3.73=2631rpm/4.30=3033rpm
3rd gear @ 40mph 3.73=2299rpm/4.30=2650rpm
4th gear @ 50mph 3.73=2174rpm/4.30=2506rpm
5th gear @ 60mph 3.73=1951rpm/4.30=2224rpm
6th gear @ 70mph 3.73=1773rpm/4.30=2044rpm

All this shows is rpm @ given speeds and doesn't take into account real world rpm necessary to move a load at the given speeds...it shows that basically the 4.30 diff will run 1 gear higher than the 3.73 at the same speed after 1st gear. You folks can take this fwiw.