At that level a plug and play ECU isn't ideal, they cater more for the bolt-on level rather than forged, high-boost set-ups. As you go over 300bhp the horses are harder to capture so a greater emphasis is on the tune. A lazy, rich map will not make power and those ECU's usually have a lazy, rich map.. I own a few so can tell you this firsthand.
You'd be looking a fully manageable unit to squeeze the extra horses out and an experienced mapper to do it for you. The mapper is the key to which management to run. Case and point - We've all seen eManage Ultimate used on big power starlets before but nowadays technology has moved on and very few local tuners will even touch them never mind map them. Find someone who is proven and let them tell you the best options. No point buying something they have no experience with.
Please bear in mind that you can quite easily be talking four figures for a new ECU wired in and mapped to your requirements. I reckon this is one of the big reasons that long term projects are broken and parted out right at the end before they have even seen full throttle.