I would be sticking in 272I and 264E cams with some slightly stiffer springs (maybe 60lb off the seat). If you can afford to have some headwork done (by someone who really does know what they are doing) then I would at least give the head some attention in the throat area, some polishing of the combustion chambers, a decent valve seat job, check the chamber volumes.
Then if you could stretch to it (and no doubt against what some people will say) I would get the ports opened a little and I would probably raise the CR a little nearer to 9:1 and fit oversize valves on both the intake and exhaust. With the ports modified to suit and the larger valve sizes you will see more torque for less boost and the raised CR will help with the spool and low speed torque. If you're not planning on running stupid boost figures (which you shouldn't anyway with the stock pistons and liners) then this will net you some good gains. If I remember you have an AEM, no doubt you're running on Optimax 100% of the time and have excellent intercooling, cooling system and you should budget for an oil cooler at some point - it might not be needed but be prepared to fork out for a kit if your oil temps go much over 110degrees.
The big unknown is your turbo system, I do not know anything about it. It may be that those turbos need over 1.5bar of boost to even get anywhere near their peak efficiency. My suggestions really hinge around a correctly matched turbo kit. If the kit is good for 900bhp you might be a little disappointed with the trade off in spool time copared to torque figures running daily boost of a max of say 1.25-1.3bar. At least with a decent valvetrain you'll be able to venture a little higher rpm wise, increasing the powerband for those big blowers! I hope it all works out well though, looking forward to the results.
By the way, I know a great head guy in the US and am back and forth a fair bit with parts etc. If you want some contact details or at least someone to discuss things with pm me and I'll give you his details. Although, you're probably not a million miles from people who can do the work you want though are you! Anyway, just let me know.