personally, i've always been a huge fan of the kumhos bc i think they're excellent bang for the buck. i have never owned a set, but have had numerous friends that do and they all love 'em. next choice would probably be the falkens based on all the rave i've heard about 'em form the autocross guys.
if you're just doing normal driving, i think the treadwear rating would be your largest concern. just go with whatever says it'll last the longest.
The T1S is the top of the line in the toyo lineup. This is the number one all around tire of Miata enthusiasts. Its used as a spec racing tire by several race organizations and does everything well. The Kumho MX is getting alot of great PR and is a better pick than the 712. And everyone knows about the Falken Azenis. Its the best performance tire in the Falken lineup. Nothing outperforms it specially when price is factored in. Downside is its poor wet performance, it wears out quickly (15K tops with moderate driving) and comes in limited sizes. I have seen a set of azenis completely transform the handling of a car with no other mods.
I've Heard Alot About The Kumho MX. Seem's Like Alot Of People Say The Kumbo 712 Are Great. Not To Many People Have The Falkens, So Its Hard To Get Opinions. As For The Toyo's, Seem To Be My Choice So Far. Treadware On All Are Equal... Im Looking For A Decient Wet Traction As Well. We Do Get Alot Of Rain. Also Like A Little Show As Well... The Toyo's Has That Nice "V" Tread Pattern. Gotta Make My Friends Jealous Cuz They Dont Mod Their Cars... [8D]
you can get a set of Goodyear Eagle F1 GS-D3's for pretty close to the same price. (great tire, and has gotten even greater reviews from several magazines and Tire Racks personal assessment as well. One of the other great things is a much better tread wear than any of those)
You can see on the bottom of this page customer reviews as well as the overall rankings of people who have purchased the Goodyears...it was ranked 1st out of the 18 tires that Tire Rack carries in the Max Performance Category. This category includes the Kumho MX tires. which are $20 a tire cheaper, but only ranked 7th out of the 18. The price obviously depends on the size of the tire you are looking for also, as some tires will not even have the load bearing capacity that is required. Something that everyone should pay attention to, if you overload your tires, you will get extremely poor performance and tire wear.
This shows a side by side comparison of customer rankings, price, and ratings for the Goodyear versus the Kumho. The Kumho is only an Ultra High Performance tire, where as the Goodyear is a Max performance (the highest category), obviously the difference here in price is substantial. Most notable to look at is the poorer tread rating marks.
Here is a comparison of three Ultra High Performance Tires...
all depends on what you consider overkill, for the price you are really getting a much better tire for only slightly more, you get excellent traction capabilities, and a treadwear that seems way more favorable than the 712's. I agree, this is a Y rated tire...and the chances that my car will go over 189mph are nil, hell they aren't even chances, there is no way my car will ever go that fast. At the same time, all the traction and handling capabilities are greatly improved over some of the lesser tires. However, he did say normal summer driving, so it probably won't make much difference for him. The only other thing I can say is that for a Max Performance tire, this thing rides extremely nice, it is smooth, and quiet, alot quieter than my girlfriends 712's on her Tiburon. As for overkill...well, I heard alot of people say my 17's were overkill, then I heard alot of people say that brembo slotted rotors and stainless lines were overkill, I mean after all it's just a focus. All depends on what you want in the tire...You can spend a little less and get a little less, or spend a little more, and get arguably the best tire out there right now. I say arguably because the numbers show it, these F1's are amazing but personal opinions differ, which means arguing ensues.  I was just giving you my thoughts, get the tire that suits you best. Most importantly have fun driving.