Typically the speed rating of a tire is ultimately going to come down to the rubber composition, and therefore will have not only impacts on the maximum safe speed but also on the handling and the treadwear as you have found.
Higher speed rating tires are made with softer rubber compounds, which can better handle the increased heat and stress at high speeds. Lower speed ratings will be made with firmer rubber compounds which increase long-term durability at the expense of road noise and handling in severe weather conditions.
In practical terms, what you're going to find is that the 'T' rated tires are not going to perform as well on wet roads and in light snow, especially for a car of that weight. We have T rated tires on our Odyssey - ones that are technically designed for light trucks - because the vehicle is so heavy (over 5klbs empty). Softer tires would be quieter but would wear too quickly. The weight of the van helps to put more pressure on the tires and somewhat negates the concerns about poorer inclement weather handling, although some of that is also because the tires we have are M+S rated (mud & snow).
The biggest benefit you'll see is that they probably will last pretty close to the 75k mark, with proper inflation and regular rotation. As you get into the miles they'll definitely be noisy. in the first ~5k miles they'll also be particularly stiff and may be prone to wandering and tracking as they get broken in.
If none of this concerns you, then definitely go ahead and use them. In the future, I would recommend not purchasing tires from Amazon, as of late I have a hard time feeling confident in purchasing even name brand items from them. I usually try and recommend Tire Rack to folks, as their prices are nearly always as competitive as any of the other major retailers, they have excellent customer service and warranties, and they have one of the biggest selections of tires for most vehicles.
