This is a different kind of enthusiast forum from, say, the '94-'96 Impala SS Forum.
They've been making their full-size sedans considerably outperform OE for the last 25 years.
The enthusiasms I encounter most often here are for original equipment.
The few people in this forum that want more acceleration, sharper handling, or quicker braking from their Tahoes / Suburbans tend to be the exception, not the rule.
The only thing I know for sure is what you already covered in your first post regarding the RPOs that start with 6 & 7 corresponding to the front springs.
We don't even know how similar or compatible our torsion springs are to the GMT400 or GMT900 springs. At least that would open up our options considerably.