Sorry guys, did a couple of different searches here. And the Subaru website wasn't specific, nor some other auto makers.

I am assuming the regular Impreza WRX uses regular octane (85-87)...

And the WRX STI uses the premium (91-93)...

Is this correct?

Sorry again for the newb question, but I do not own either.

Thanks for any quick answers, and mods can close/remove if needed (but please after I find out lol).

 

91 and high for both WRX and STI.

I'll try to find a link.

 

Starting and operating Fuel
Use of a fuel which is low in quality or use of an
inappropriate fuel additive may cause engine
damage.
�� Fuel requirements
�� 2.5-liter non-turbo models
The 2.5-liter non-turbo engine is designed to operate
using unleaded gasoline with an octane rating of 87
AKI or higher.
�� 2.0-liter turbo models
The 2.0-liter turbo engine is designed to operate using
premium unleaded gasoline with an octane rating of
91 AKI or higher. If premium unleaded gasoline is not
available, regular unleaded gasoline with an octane
rating of 87 AKI or higher may be temporarily used.
For optimum engine performance and driveability, it is
required that you use premium grade unleaded gasoline.
�� 2.5-liter turbo model
The 2.5-liter turbo engine is designed to operate using
super-premium unleaded gasoline with an octane rating
of 93 AKI or higher. If super-premium unleaded
gasoline with an octane rating of 93 AKI or higher is
not available, premium unleaded gasoline with an octane
rating of 91 AKI or higher can be used. For optimum
engine performance and driveability, it is recommended
that you use super-premium grade unleaded
gasoline with an octane rating of 93 AKI or higher.
�� Fuel octane rating
This octane rating is the average of the Research Octane
and Motor Octane numbers and is commonly referred
to as the Anti Knock Index (AKI).
Using a gasoline with a lower octane rating can cause
persistent and heavy knocking, which can damage the
engine. Do not be concerned if your vehicle sometimes
knocks lightly when you drive up a hill or when
you accelerate. See your dealer or a qualified service
technician if you use a fuel with the specified octane
rating and your vehicle knocks heavily or persistently.

 

Both cars require the use of premium fuel with a minimum R+M/2 octane requirement of 91, but the STi may run better with 93 octane. Both cars can use regular gasoline with 87 octane but the knock sensor will sense engine knock almost immediately when load is put on the engine and pull the ignition timing way back to safeguard the engine. These cars were designed for use with premium fuel and will run horribly with equally bad fuel economy if lesser fuel is used.

The same requirement goes for any factory Subaru turbocharged engine, including the Baja Turbo, Forester XT, and Legacy GT.
Above quote from Shiv Pathak of Vishnu Performance Systems.

--
0==WW==0
"…axles of evil…" - george w. bush

 

Oh man, really appreciate your help guys...

I wanted to confirm if I was wrong in my assumption and so I am.

Once again thanks.