This is from consumer reports:
Speed rating. This letter denotes the maximum sustainable speed and is found directly after the load index. For S-speed-rated tires, it's 112 mph; for T, 118 mph. Speed ratings for other tires include Q, 99 mph; H, 130 mph; V, 149 mph; and Z, 150 mph plus. While such speeds may seem wildly impractical, tires with higher speed ratings tend to provide better handling at legal speed limits. Except for winter tires, choose tires that have a speed rating at least as high as the one specified on your vehicle's placard and consult the owner's manual. Speed rating may vary by size."
Personally, I'd be more concerned with the tire itself than the speed rating. I've had one set of Hankook tires. They were Dynapro ATMs. They looked great. Agressive tread, good traction, they were great in snow, but I couldn't keep the things balanced and led to shakes and wobbles at highway speeds. Then I started reading reviews (should have done that first) and saw that this was a common problem. I know it's a different tire than the Ipike, and they were on a pick-up truck, not an SUV. So my suggestion is to definitely read reviews BEFORE you settle on a particular tire.