Ask Mr. Smarty Plants

What Mr Smarty Plants likes to do is recommend that you check out the recommended species list for North Central Texas.  You can sort through the list- so you can select trees of the height you prefer and start to consider options.  I found 13 trees when I looked for those in the 36 to 72 ft. height.

Unfortunately, "faster-growing" and "last for decades" are slightly contradictory.  Some fast growing options are Acer negundo (Ash-leaf maple) and Ulmus crassifolia (Cedar elm). 

Some Oaks also grow relatively fast.  Quercus muehlenbergii (Chinkapin oak) and Quercus texana (Nuttall oak) are quite attractive, Quercus texana (Nuttall oak) may do better in your clay soil.  If you are willing to wait for your tree, magnificent varieties such as Platanus occidentalis (American sycamore) and Carya illinoinensis (Pecan) do well in your region, but are probably a bit tall for a yard the size of yours. 

 Is there a problem planting them where the pears are currently?  Well, a little.  Are the pears still there?  If so, the roots will continue to compete for water for some time.  Make sure you remove the stumps and, if you can, you will want to start your new trees outside of their existing dripline, just to minimize the competition.  Similarly, you noted you want a less dense tree with better curb appeal.  All of those recommended above will produce a very attractive tree.  You can improve density and curb appeal by judicious pruning and raising the canopy when it is mature enough.