I purchased a Rigol DSA815-TG (1.5GHz) several years ago and have been very satisfied with it. I recently purchased a DSA875-TG just prior to the release of the RSA5000 Series, and have been even happier with it.
The fasted sweep time on the DSA815 is 10 Ms, whereas the DSA875 is 1 Ms, and additionally goes up to 7.5 GHz. The Rigol RSA3000/5000 Series with Real Time display is available. Although I'm very satisfied with the DSA875 that has a higher frequency coverage than the RSA Series, at significantly lower cost. While they both (RSA and DSA875) have a 1 Ms maximum Sweep Time in the conventional sweep spectrum mode. The DSA875 continues to meet my requirements and interest without the Real Time capability of the RSA Series. Yes real time SA is very nice for analyzing PLL lockup, Frequency Hopping, unique modulation formats, etc. Although for most applications it isn't needed for basic RF performance tests, EMC/EMI analysis, or hobbyist activities. And it certainly isn't beneficial enough for me, to justify its additional expense.
I believe that hopefully (and per Rigol comments) the DSA875 will continue to be supported, and in the near future I will report on DSA832/875 Firmware version 00.01.06.00.03 that I have been reviewing (see 'Reply #4' below).