Right'o.
What BHP will the engine be producing after rebuild?
Are you using the rolling road or normal driving method for bedding engine in?
I've asked a technical chap to advise me on your situation, I told him you will most likely use the normal road use to bed the engine in. This is his reply:
CRO 10/40 for 500 miles, using the BMEP (Brake Mean Effective Pressure) to run-in your engine. You want to use your 'torque' band to build up as much pressure behind the pistons as possible. This may mean loading your boot with heavy bags of sand or simply getting 3 large friends to sit in the car as you drive it. Don't bog the engine down, use a nice steady band of torque but excessive reving is not required. (if you have had a RR graph already you should be able to work out where this band will be in relation to RPM)
After 500miles of the above he recommends something like Millers Maxifleet 10/40 which is a good quality semi-synth with a good additive pack to bed the engine in for a further 2,000 miles. Still using your torque band but increasing the revs as you get past the first 1,000 miles, use your upper RPM's and make your engine scream as you get close to your final 1,000 miles on Maxifleet 10/40.
Finally replace the Maxifleet 10/40 for your choice of full synthetic (if your running plenty of BHP and doing some hot weather track days) then use a competition full synthetic like the CFS 10/40 which has a tri-ester blend and includes a low friction ester to minimise power loss. If you are using your car for more eco purposes then a full synthetic 5/30 (VAG 504.00/507.00) will be fine and cheaper than the CFS 10/40.
Hope this helps.