I don't much buy the "it'll look dirty with time" argument. Only if you're slack with what I would consider normal upkeep, regardless of top color. Use citrus-based products for sap or bird dropping removal, and just wash it well with the same soap you do the rest of the car with. I've had WHITE tops that stayed tidy and crisp for years, with no real out of the ordinary elbow-grease on my part. Just considerate care.
Do an honest self-assessment of how clean you keep your vehicles. If that self-assessment dictates a black top, go black. But if your nature is to stay right on top of things, go with what visually pleases you. The grey top should look super for years, as long as you use common sense with it.
Whenever I'm strolling through our local dealer's service bay, I see SCARY SCARY upkeep and maintenance and care of customer's cars. It makes me cringe, as I always dreamed of being able to buy a brand-new 911 since I was a small boy, and can't imagine achieving that goal in life, and then taking it for granted like a doormat. Filthy interiors, door sills that look like they're used as cowboy boot mud-scrapers, scratches, wheels with a year's worth of brake dust accumulation, etc... People who have the money and driving enthusiasm to buy Porsche, but don't have a whif of pride or awareness when it comes to caring for the car itself. It's like they've never in their life understood what it's like to NOT be able to afford such wonderful things. Dealers see these scary cars day-in, day-out. That's the foundation of their opinions when they say "don't order the gray top", because they see all the trashed cars roll in and out of the service bays. For all they know, you're just another one of those scratch-a-big-check-and-go-on-your-merry-oblivious-way customers.
I think the combo you originally ordered looks RICH and classy. I also know that this subject is driving you to borderline lunacy!!