Rex;
There are lots of variables that come into play regarding tires at Bonneville. I haven't finished my car yet so I can't speak from first- hand experience but I can point out a few other cases that may be germane.
Sports racing cars routinely ran 240mph- 250mph at Le Mans and at Spa- their tire widths were enormous. I suspect the difference you found might be influenced by differences in rolling resistance, actual rolling radius at speed (how much tire growth was there?), rubber durometer, and the tread pattern. Wide slicks might not hook up well due to the thin layer of loose salt that exists on the surface most of the time. Under those circumstances a tread pattern might help but narrow LSR tires exhibit a greater pressure on the salt surface (lbs per sq inch) and may have better traction due to crushing the loose salt layer. I doubt that there is one choice with an advantage under all circumstances.
This is just my idle speculation- Goodyear may have actual test data somewhere.
I had an opportunity to talk to factory tire engineers from Dunlop and Pirelli at a Superbike Championship at Laguna Seca some years ago. They were very skeptical of narrow LSR tires' lateral stability and thought that, all else being equal, a wide tire should give better handling even at high speed. I'm reasonably sure those engineers had no LSR experience so how much credence their opinions had is uncertain.
One thing is for certain-- some measure of F & R down force will be necessary for both traction and stability.
Regards, Neil Tucson, AZ