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MA70-3.0GT, fuel controllers aren't essential but they're a very good idea and I wouldn't try for that level of power increase without a basic SAFC II at the minimum. Just because a 550cc/m injector flows 125% of what a 440cc/m injector flows it doesn't mean they flow the same amount at idle, low load, mid loads, or even high loads. You may waste fuel, lose power or in some odd cases find that the 550s flow LESS at low or mid loads. Depending on if your ECU is setup to still run closed loop you could spend a lot of time running quite poorly (whenever the system is operating in open loop). A fuel controller isn't going to change the fuel cut level, that's determined by factors such as the duty cycle of the injectors (which IS affected by the size of the injectors).

Ochowdero, sure there are simpler piggybacks than the MAFT Pro or MAP ECU, etc. There are a lot of simpler devices with fewer functions and a ton of support... I'm sure you've hear of the SAFC, SAFC II, NEO all by Apex'i. These are just fuel controllers, the list is quite long. The functionality varies per device, some support data logging and some will integrate with an on-board wideband which I also strongly recommend (and it's essential if you're looking to tune on your own). There are independent units for timing control and boost control. The 'super piggybacks' roll all of these into one package which uses one app for data logging but often at the expense of a steep learning curve.