Depends on how far you want/need to go. The Saab EV-1 concept car of 1985 (which was entirely based on c900 running gear) peaked at 285 hp @ 6,500 rpm, where the T16 normally reaches peak power at 5,300. That 1,200 rpm difference alone makes for 20+ % more power at the same torque level (Peak torque on the EV-1 came at 3,500 rpm and was an entirely reasonable 246 lb/ft or 334 Nm - even the 1985 Saab 900 5-speed installed would have a fighting chance to survive at that level!).
Apart from strenghtened rods, bigger intake ports, and low compression pistons, the engine consisted out of stock parts. Crankshaft, camshafts, valves, valve springs and the castings were all factory standard.
The hydraulic valve lifters in a Saab 16v engine are good up to 7,200 rpm. At that level, balancing the rotating assembly and shot peening the con rods as well as the crank are all that's needed to cope. Billet cranks will only be needed when aiming for 400+ hp, and at about 600 the cylinder head bolts will have to run all through the block as per Per Eklund's car...
The turbo is rated for a certain efficiency (about 70% is generally accepted to be within limits, the rest is being converted into heat) at a certain amount of airflow (say 20-40 cfm) which corrsponds to an attainable hp level within a defined efficiency range. Whether this airflow (for a given capacity and volumetric efficiency of the engine) will be reached by a combination of low rpm and high boost, or the other way round, it doesn't care. It will still provide the same efficiency at the same power output.