I don't know if anyone can suggest "the best" tire for you 99 XJ8 VP since this is another very subjective issue. All I can tell you in my two years of being a Jaguar owner is that my 99 XJR came with new BF Goodrich 255/40ZR18 95Y tires, which as J.C. Conway mentions, are an inch taller the tires on the VP.
They have a very aggressive dry road tread pattern that I enjoy on dry roads! A bit unsure of on wet roads. And are useless in snow! And I also agree that very few of us drive at speeds requiring Z-rated tires. When I buy my next set I would opt for an all weather tire, depending on your usual driving conditions, and find a good tire dealer who's experience and advice you feel you can trust. Then weigh your decision on what the dealer suggests would be best suited for your needs and the one you like the looks of best.
P.S. Lean toward a trusted dealers advise, and also I'd suggest passing on anything they try to push as "on sale".

Submitted by vogelbp@gmail.com on Thu, 02/16/2012 - 17:43

I have Kumho Solus KR21s on my '99 XJ8L and absolutely love them. I also have them on another much larger, heavier car and they've performed flawlessly there as well.

I've also liked the Toyo Extensa tires on another of my cars and have no reason to believe they wouldn't perform well, too.

If you obey the speed limits (or even exceed them by no more than 25 mph driving for hours on end) you can choose virtually any of the speed ratings available in tires that fit these cars with no issue. I have yet to see any in the appropriate size that don't have a sufficient load rating, either.

Submitted by jcc@majure.com on Wed, 02/15/2012 - 15:25

On my 03 XJR I recently installed Michelin Pilot Sport A/S Plus 255/40ZR18 95Y M+S tires. (Don't know what half those codes stand for!) I have been happy with them. Your VDP would have 17 inch wheels instead of the Rs 18, but it's hard to go wrong with Michelin tires.

Submitted by stevejag@sbcgl… on Wed, 02/15/2012 - 14:28

I'm a believer in Bridgestone Turanza's, in the H, S, or T rating. The Turanza Serenity in H speed rating has received really good owner reviews. I had a set on a prior '93 XJ6, I have them now on our Volvo Cross-Country and as winter tires on the XJR. Smooth, quiet and every one of them has worn perfectly square. Needless to say, I like 'em.

No one needs a Z rated tire for a nice smooth touring sedan.

Good hunting!

Submitted by r.e.rogers@usa… on Wed, 02/15/2012 - 14:08

Help, our old tires have worn out. We are not going to drive it 100 mph but do want a very comfortable ride with excellent traction. What do you guys recommend? The more options the better. Thanks so much, RER

PS As a mimumum please discuss Goodyear, Michelin and Bridgestone.