I run a 4.86 gear with 9"x30" tall Hoosier lightweight radial slicks and a 2.71 low gear 904. But radials don't grow much on the top end so rpm's are higher than with bias ply slicks. I don't recall what the difference was when I switched years ago. Radials are faster but more sensitive to track conditions and will spin easier. It running out of breath at the finish line turning around 6,700 because I have unported stock heads. I leave between 3,000 and 3,500 footbraking and my converter flashes to 5,100-5,300. (Autometer playback tach shows actual highs & lows instead on one having to remember what they "think" they saw for converter flash, shift points, rpm drops, etc.)