I think you're right about Spectre topping 400, but as I recall that was at the Shootout, rather than Speedweek, World of Speed, or World Finals.
In FIA-sanctioned meets, there are no separate classes for gas or fuel. They're all lumped together, so there's no way of telling what they were actually using.
The fastest "gas" record currently in the rulebook for SCTA-BNI was set by Spirit of Rett (AA/GS) back in 2009 at 368.136. Spectre still has the A/BGS record of 356.645 from 2010.
So, it looks like the bragging rights for "gas" now belong to Costella-Yacoucci-Waters with their new 384.657 record.
Jeff in Boise