Running K04s on K03 code does NOT require a 5bar FPR. This is only needed if you want to max out the stock fuel system. The overboost issue may not even occur with all setups (I have no 1st hand experience here...), and likely wouldn't occur with more conservative software that ramps boost more slowly (MTM, etc).

It's all about compromises, but you have to weigh both sides of the equation. K04s provide better reliability due to decreased shaft speeds, the potential for more power down the road, and lower IATs. The only tradeoff is the *possibility* of adding an MBC in parallel. IMHO, the benfits far outweight the drawbacks.