As a SL Dealer I am able to offer the opportunity to hear both the 545’s and the 845’s.Both with all the current SOTA features and “high end” electronics. The 545’s are located in San Francisco in a room of similar size to yours. The 845’s are in a much larger room.
At my “Ranch” (2 hours away) I have a pair of 845’s. There is a SL “sound”, but also different and shared characteristics. I love them both but for different reasons. Of course room acoustics are a big factor, which complicates matters.
And, of course, there is the WAF!
Weather or not you should move up is a very personal decision. Bigger my be better, but not necessarily!
Best, if you can, come listen to both and decide for yourself!