I wouldn't worry about the staggered sizes.  The tires will go bad from age long before they wear out.  Typically you can get maybe 7 years from a set of tires, then they should be replaced for safety.

I run Summitomo HRTZ IIIs on my fun cars.  They are quite reasonable, quiet, and seem to provide decent handling and traction.  A set for my Mustang is like $350 plus like $100 for mounting an balancing. 

I would not count on being able to run a 245/45R17 on the front of a '66.  I am running 245/40R17s on my '67 because once I finally did the Shelby/Arning drop my 245/45R17s rubbed, and I'd already tweaked the fenders as much as I could to get them to fit without the drop. 

In the rear, I'll defer to those who have the earlier cars.  I'm running a 275 on my '67 on a 9" rim, which just barely fits, and I'm actually considering going a little smaller or making some mods to get some more clearance because the harder I push the car I've encountered some rubbing that wasn't immediately evident on installing the wheels/tires. 

I am using 17x8's all around with 4.75" backspacing.  I have 245/45's in back and with this backspacing and with rolled fender lips, it is tight.  With some more backspacing - 1/2" or so it would be OK on the outside but close on the inside with a convertible.  255's might fit but it depends a lot on your backspacing and I'm not sure what you gain.  Without rolling the lips, things are going to be tight and you don't want to cut a tire.

In front, I am running 225x45's.  These are also a bit tight with these wheels.  I clear well in back but in the front edge in particular it is close.  Much depends here on your alignment setup and upper control arm shimming.  I think more than a a few folks are running 225's so it is certainly done.  Based on some advice from a neighbor I did a fender modification that is not an option for a completed/painted car.  I cut a thin wedge half-way around the fender lip to give me the clearance I need in front.  I will also be rolling the fender lips when I have completed my rust repairs.  The first picture shows my initial clearance on the front corner and the final after the mod.  This area is a common area of contact with wide tires and/or lowered suspension.

TKOPerformance wrote:

I run Summitomo HRTZ IIIs on my fun cars.  

I'm fine w/ directional tires, but not really keen on asymmetrical tires.  If I can get the Summitomo HRTZ II in the size I want I'll probably go w/ those or BFGOODRICH G-Force Sport Comp 2.