I’d say that your current 3.23 ratio is pretty much ideal for your purposes.
My 2002 WS6 T/A has that same exact rear gear behind a 4L60E (electronic version of the 700R-4) and with the factory 25.6” tall 275/40-17 tire is sees very close to 2100 RPM at 70 MPH. My car is of course equipped with a lockup converter, it’s completely factory stock.
Your 28” tire would run at about 1920 RPM at 70 if you had a lockup converter so being non-lockup you’re likely to see close to the 2100 I’m seeing at 70.
That’s a nice cruising gear for the freeway, and you’re going to have plenty of around town acceleration fun with that 3.06 low gear. The big Pontiac torque will nicely make up for the somewhat wide spread between that 3.06 low gear (that’s really best suited to small-blocks) and the 1.62 second gear.
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1964 Tempest Coupe LS3/4L70E/3.42
1964 Le Mans Convertible 421 HO/TH350/2.56
2002 WS6 Convertible LS1/4L60E/3.23
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