Keep in mind that Xfce on Solus is a work-in-progress, and probably hasn't been built for release yet. So it's probably not as fast and efficient as it will be when all its compiler/linker optimizations are enabled. Just guessing, but that's the way it worked with the Windows software I built for a long time. On my main laptop it's decidedly slower to start up and shut down than the Budgie DE it replaced, so I suspect it's the same situation in Linux. I suspect it will run leaner and cleaner once a release version of an .ISO file is made available.
I have the same model ACER Travelmate as you do, bought for motorcycle touring. (Great little laptop!) It's been running Solus KDE Plasma for years, and doing a surprisingly good job of it, so I suspect that yours will also perform very respectably wiith Solus Xfce, once it's ready. All the Solus editions perform quite well. But to test it at this time would probably be very misleading, and not quite fair to Xfce.