Trane AC+furnace model selection
I've been lurking for a couple of weeks and have had a number of contractors come over to give an estimate on replacing my 20 year old system. I had two paths to go: (1) Upgrade to a fancy future-proof system or (2) Replace system with a standard modern system. I live in Orange County in Southern California, so path 1 just didn't make sense overall given the relatively short usage of the AC and furnace throughout the year.
I live in a 1,900 sqft 3-story townhouse. The AC is outside and furnace in the attic. I've narrowed down my selection to Trane to AC: 4 ton XB13 or XR13 and furance: XR80 or XL80. None of the contractors could give me any functional differences between the XB13 and XR13 other than the shell being different colors. The website also noted the XB13 being 48,000 BTU while the XR13 was 46,500. This was explained as the XR13 being more efficient. The XR13 also has a bit more insulation to give it a minor 2db difference in sound. These three features wouldn't justify the ~$ difference, so I'm wondering if you guys would be able to help me understand the differences. As for the furnace, there's a ~$ difference between the XR80 and XL80. I'm less informed about the differences and benefits of one over the other in this front.
Also, given Trane = American Standard, I'm still open to it if the price difference is noticeable; however, I can't seem to find the exact answers I'm looking for as far as actual differences. Given the lower-end models I'm selecting, would the comparable AS models offer the same warranty? Also, I've read and have been told Trane and AS comparable units are the exact same thing with the same model # sans the brand in its nomenclature. One contractor though, has told me AS does use slightly inferior parts in its units.
Overall, I'd love to hear any thoughts or suggestions in regards to the Trane models I've inquired about and the American Standard equivalents, if the cost difference justifies any differences in warranty and "parts quality." Thank you, and I'd really appreciate any input to help me make my final decision this week.