But in the end...air temp, sunshine, overcast, track temp, track rubber, wind direction, set up, etc make it really hard to compare times from different days...let alone different tires!!
Barber is a handling track and it is all about grip.
In August 2013, running Hoosier SM6's I set the SCCA SM lap record at Barber at 1:46.735. The SM6's were the hero tire with the most grip we have ever had.
Then in February 2015 on a really cold day, running Toyos, I was able to get into the mid 1:44's in qualifying, and set the new NASA SM lap record 1:45.719 (almost a full second faster than on the stickiest Hoosiers)
And then yesterday, in temperatures over 100 degrees, running on Hoosier SM7's I was able to almost equal my SCCA lap record, and ran 1:46.798.
So while on the same day, Hoosiers will generally be faster than Toyos, as Ron said, comparing lap times from different days is often going to be misleading unless you know all the conditions