The manifold isn't a "limitation" as far as air flow or anything else goes, not at these power levels. It will absolutely lead to heat soak, which will pull timing, but there's no real reason to upgrade it at this point.
The trans will definitely start to slip at around 650ft lbs of torque or...
Melt as in the methanol will eat away and destroy the seals on the DI injectors causing a leak.
The only way to really remove ethanol from the equation is to plug the DI ports. Methanol, M5 specially that we all use as additive fuel, is -insanely- corrosive. It will destroy in the DI injectors...
My daughter is diagnosed with obsessive-compulsive. It's incredibly debilitating. It's not driving too close to trucks; it's having to run water for 9.5 seconds, checking light switches 19 times, driving around the house 4 times before we can park, waking up at 5:35am every day, and being unable...
You'd melt the DI injectors. You have to plug the ports, and you can't plug the ports, because you'd have to remove the DI injectors, removing the DI injectors freaks the car out. Codes for days.
@Jesse DaBears has a fuel cell.