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When people say timing gives big gains when tuning, I think it has more to do with the fact that from the factory, at WOT, cars will run leaner than optimal power at low rpm and richer than optimal at high rpm. When you adjust the fuel maps, you have to then adjust the timing and together those will give you noticable gains in torque.
What RobertISaar said is exactly correct, EGR "allows" more timing, precisely because it reduces the burn speed, and is less efficient not considering throttle losses.
To me it sounds like you don't really care too much about keeping your car NOx emission compliant (on that note, diesel trucks emit several orders of magnitude more NOx/PAHs/PM than cars, so it makes so much sense to regulate passenger cars tightly right?). With an e-throttle car, the way I would set up the tune if the map is not switchable and I didn't care about emissions compliance is the following:
1. Keep the highest load cells tuned for maximum power, because there's no reason not to make maximum torque while your foot is all the way down.
2. Lean out the next few cells down and increase throttle position to compensate. Control knock with valve timing if possible, then ignition timing. I would guess that the factory tune in a lot of cases is pretty close to this.
3. Figure out how lean you can run the engine at lower loads, and then set an rpm range where the engine runs lean (a 2009 car probably will need to be put into open loop for this to work), and then adjust the throttle map accordingly to get a smooth transition from lean to stoichiometric. Essentially, running as lean as possible at lower loads, controlling torque with fuel instead of air.
4. Lower the idle speed.
5. DFCO on, throttle opened fully while decelerating if possible.
6. No EGR, if that's an option.
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