haha. The correct part of your comment is 'many hours', the quality part can depend on your pre work accuracy in the virtual world - if thats not up to scratch then don't bother. Trust me its not as much fun as you think the novelty fades after a fashion. To be honest I will probably hardly use it, unless the predictions are way off or theres a nice long free gap. Saying that I think its been used twice this year.
I like the idea of this coast down test, once you make adjustments for your losses etc, use the same test point and conditions it should be fairly good results. Dump the data in to excel job done. I rather have a go at that over a weekend than setup a tunnel test.
Regards
SubSonic