[DAVID GAGNARD]

If your engine has a compression ratio of about 10.5 to 1 or less,straight 93 octane pump gas is all you need...(my street car engine is 10.5 to 1 compression with iron heads and all I've run in it is 93 octane pump gas with no problems in 35,000 miles)....I'm guessing that is about what compression ratio the Roush engines come with........

With that said, yes you can mix 100 octane low lead AV gas with any unleaded gas without any problems, I do it all the time......
I run a 50/50 mixture of 93 pump gas and 100 octane AV gas in my race car, have been doing this for 7 years.....of course no emissions/cats and a carbed engine........

David