I have a very similiar combo and made 494/513 with the mods/parts in my sig...same crappy 91 octane fuel.
Don't have the dyno sheet yet. Apparently the bypass valve that's on the drivers side of the blower is not opening and/or not sealing properly. From what i've read this can cause the air to cavitate in the blower causing power loss. Hopefully this is the problem. Anyone ever heard of this happening?