+1 for ARC
I have went through many line stages over the past 5 years that included the LS 26 & 27. I would not recommend simply looking at them in the sense of the number as your sequential options. I would stay within a generation. For example, the LS17 & LS26 and then the LS17SE and LS27. The 27 was a significant upgrade over the 26 and the aesthetics are nice upgrade as well if that appeals to you. I never had a 17SE but have always heard and read they were quite impressive.
Like most of the top brands, these older models hold their value quite well. I believe you could find a 17SE for around $2000 and an 27 for around $3000. These prices haven't changed much in the past 4-5 years and won't likely drop significantly anytime soon for one in great condition. This all to say, try one if you find it and if it turns out to not be the sound you are looking for...sell it.
Good luck!