If cruising the highway comfortably is a priority the 3.08s are tops, but a 350 or 400 likes a little more gear.
With the smaller cube engine go with the 3.23s for the best compromise between acceleration and highway RPM.
The 3.23s are probably the most common performance gear that came in the majority of musclecars, regardless of car brand.
I had a '69 400 Firebird 4-speed coupe and the original gears were 3.23s. I can remember street racing against a 383 Road Runner back in the late '70s, it had 3.23 gears too. I beat him with my 1756cc 1957 VW that ran in the low-14s.
