It would seem doubtful that there would be a large upgrade in system transmission with Starbright XLT vs. UHTC, but Celestron's old marketing (with test curves) made a claim of 6% overall for visual for XLT vs. UHTC. https://www.optcorp....OPT/EDU/xlt.pdf I don't know if Meade has changed their UHTC since then, or if the original test was accurate or representative. There was some substantial improvement from Celestron's original Starbright that preceded the XLT, again per graphs. http://www.celestron...-coating-system My old 8" is of the older Starbright coating type, so for a similarly figured SCT with the newer XLT I could calculate taking a hit (16% claimed, or an effective difference of 2/3 of an inch of aperture--note that it wouldn't impact resolving power but instead the ease with which lower surface brightness/dimmer objects could be detected.)
As others have noted, if you are considering the differences in light transmission you should also consider the other parts of the optical train including whether or not a diagonal will be used (e.g. a refractor, SCT, etc.) and what type. Of course, buying a better quality diagonal than what comes stock can also improve light transmission to the eyepiece. Eventually, for a given scope one is likely to upgrade to 2" diagonals from 1.25" stock to allow use of 2" eyepieces. So there is substantial cost to consider there as well with only a minor improvement in overall reflectivity. One advantage of the newest/highest transmission diagonal coatings is their durability. If looking at a Newtonian you are set if it has a 2" focuser...unless you plan on a coma corrector.
Then as others have noted if you are still comparing light transmission you can calculate how much is lost to the central obstruction of each type. This diameter can typically be found in specs posted somewhere, although not always. Sometimes only secondary mirror diameter is given without accounting for the holder.
Having said all that, I'm not sure why anyone would complain about the higher quality coatings now available (standard?) on the same scope type. You can get the same tube with better coatings now for about the same price as 20 years ago.
Really what is likely to matter more to you is which type and size of scope best fits your needs for portability, travel, visual/photography, physical storage, Goto, etc. Length, bulk, and mounting systems are often limiting factors in the end choice for any given user. There is so much to learn that it is probably best to start by describing how you plan to use it and then soliciting some suggestions and comparisons.