George, I should mention that before I grew-up and got a real career, I spent a few years of my life in the "high end" wheel and tire business, so I consider my opinion to be an educated and experienced one. Accordingly, the biggest mistake most people make is going too big. I'm not referring specifically to Pantera owners but car owners in general.
One point you made is extremely important when selecting tires and it applies to every make and size. That is, tire width specifications should be taken with a grain of salt. One manufacturer's 335 width tire could be +/- an inch different in width when comparing it to another manufacturer's 335. Sidewall design and stiffness, combined with differences in tread width, all contribute to these differences which the specifications don't necessarily reveal. I have Hoosier Autocross tires on my Pantera and they're so wide I can't imagine how Hoosier had the nerve to publish such inaccurate specs for these tires.
As far as the all-season radial matter is concerned, it's still my opinion they are totally unsuitable for use on a Pantera. They simply do nothing well, except be quiet and last forever. There are some summer tires that work quite well in the cold, such as the outstanding Michelin Pilot Sport PS2. I know this from personal experience as I live in the Pacific Northwest and have a set on my daily driver. As long as it's not snowing, they work great, even in sub-zero temperatures.
In 2009, Edmonds and the Tire Rack got together and ran a test with summer tires, all-season radials and snow tires. They tested all three types of tires in the dry, in the wet and in the snow. Here are a couple of their conclusions:
" no single tire type excels on all surfaces, and the differences between each are sometimes striking. These differences are so massive, in fact, that we feel that certain generalizations can be extrapolated from our small trio of carefully selected test tires.
To the surprise of exactly no one, our winter tires dominate in snow and the summer tires dominate in the dry. The eye-opener here relates to wet performance, where a well-developed summer tire embarrasses an all-season tire made for the same car by the same folks. Anyone who never sees or visits snow would be very well served by summer tires for year-round use". They went on to say "in delivering this capability (part-time snow tire), all-season tires sacrifice a noticeable bit of dry and wet performance. Meanwhile, snow and summer tires provide clear benefits to those who can use them. In this particular test, at least, all-season tires live up to the old figure of speech our old dad used to trot out on occasion: "jack of all trades, master of none".
By the way, I've driven my Pantera in the snow (long story) and can attest to the fact it's not a good idea :-(