shrubs,

If you download this Philips Silhouette brochure, you can see the published data on page 9 for lamp current, wattage, lumens, and efficiency under several different power scenarios, using the 54w and 80w T5's:
http://britelite.com/pdf/t5_brochure.pdf

I actually graphed this using Excel and extended the data a bit beyond what they published, but I do not have the spreadsheet here at work. I was going to try it, but haven't yet.

Zink

Thanks Zink. My interest is mainly academic, but I was wondering what a real world ballast would do and how well the tube would hold up under the load and heat.

shrubs,

Earlier today I Googled "overdrive T5" and came up with a bunch of REEF/FISH TANK enthusiasts who had OD'ed 54w and 80w lamps. They had a lot of stories, but not hard data. They used mostly IceCap and Workhorse ballasts, if I recall.

Zink