RE: Ultra Sport decisions...
Anotherhobby,
If you are seriously leaning towards using your OS 70SII, then I'm afraid you'll have to build a US 40. IMHO, you will not be happy with your OS in a US 60, no matter how light you build it. On the other hand your OS on a US 40 would be an excellent combination.
Good luck with your decision and your kit building. If you run into any problems while you are building your kit, just post a question here and you will get excellent advice on how to resolve your problems, and the people here on RCU are more than willing to help you out.
One last thing. I'll second JCB's comment. Retracts are a MUST!!!