Taking advantage of the 80° Florida weather with Don on the phone in his 91LE, with his IAT disconnected the scantool thinks the temp is 61° (the PCM 'cold' operation limit), and with it connected it reads 80°.
Sensor disconnected (tricked to 60°) Don achieved timing advance of 48° (max peak 49°) with TCC lockup. Unlocked was also 48° if he feathered the throttle.
Sensor hooked up and reading 80° IAT temp, timing advance was 44° max. That'* a difference of 4° of timing advance which roughly equates to 12hp.
HOWEVER, we don't know what would happen long-term with the PCM, which is the question. It would appear that in hotter weather, there would be a greater delta (difference) and that more hp could be gained with hotter air temps (ambient).
Silverbullet and I can't test this for confirmation as our ambient air temps today are in the 40'*.
The OBD2 and the L67'* (both gens) will probably be more restrictive in timing advance due to risk of KR and emissions.