With my combination and 110 octane (no alky) I found the fuel pressure fluctuated in 3rd gear. This was on an 11.10 @ 122 pass. So to be safe I would say very low 11s or upper 10s should be the limit.
I know others have been faster on a single 340. Car weight, alky, fuel pressure and injector duty cycle all play a part as to how far you can go.
I would keep an eye on the fuel pressure, EGTs and of course "knock" to see how far you can go.
Don