Before you jump into a high SEER unit, you better pay attention to EER because you live in Texas which is not a SEER state.
First, let me explain...
SEER on a single stage unit is measured at, for argument's sake, 82 degrees outside and 80 inside. Seer for a multistage unit is measured at what is called the "Bin method". Now they test it at 80 inside but they test the OD temps at 57, 62, 67, 72, 77, 82, 87, 92 and 97. However 70% of the weighted results come from 82 and below. only about 5% come from the 92-97 degree range. How efficient is a system when it's below 77 outside and 80 degrees in the house? Pretty efficient, as it spends a good percentage Off! and off cycles are included.
California, after dealing with rolling brown and black outs has found that SEER has done nothing to reduce the energy requirements of the state. They have sued and now the law requires EER to be posted along with SEER. EER is your hot weather efficiency, SEER is your mild weather efficiency. Living in Texas, I suspect you are concerend with hot weather efficiency.
I will tell you this, look at EER for every system you are considering and then look at the cost. I suspect you will find that you will get a 16 SEER unit that will perform very admerably against a 18+ SEER system when it comes to EER at a more reasonable cost.
Somehow, this industry is racing to produce the highest efficiency mild weather air conditioners and now that EER's are being included, you will see a change in attitude as more people are educated (including contractors).
Also, be careful with the matches on a system advertised at "high SEER", putting a number in the "model" is a means of letting you assume. If I call my unit the 19BDE or the 21SFE you will assume the 19 or 21 is a legitamate SEER or EER standard, it's not. It never was and never will be. I was thinking we should market a 13 SEER system as the 25FU series just to watch the goobers flock.
I'm on your side here, just suggesting buyer beware.