The viewer gets faster as time passes. I just made a benchmark between v1.26.24.23 (released on 2020-06-20) and today's v1.28.2.37 and got these figures (with the exact same settings and in the exact same conditions, of course; in particular the new version, which got EE rendering, was set to the WL rendering mode to match the old version's render pipeline):
In my skybox, with 3 alts of mine on screen:
- v1.26.24.23: 555fps
- v1.28.2.37: 780fps
That's a +40% speed gain in light rendering conditions (i.e. we mainly measure the gains obtained via the C++ code optimizations in the main loop, outside of the render pipeline).
At ground level (in main land, 256m DD, just in front of the door of the Cool Shop, looking at its forest):
- v1.26.24.23: 103fps
- v1.28.2.37: 120fps
That's a +17% speed gain in relatively heavy render conditions (the forest got a sh*tload of alpha textures because of the trees).
Conclusion: if something slowed down for you, that's certainly not the viewer's fault... All those "minor optimizations" you can see listed for almost every release's notes are piling up over time and end up as quite significant speed gains over years...
Of course, if you look at several years back, things changed a lot *in SL*; you now got materials, Bento avatar skeletons, animeshes, EE rendering (not recommended for weak GPUs such as Intel's), etc... Plus, people with more powerful computers keep buying more complex outfits that put a higher load on others' viewers than in the past.
Also, something could have changed on your system... Mitigations (they can really kill a CPU performances) ?... Some other programs running in the background ?... Bad cooling or bad power management settings (your CPU advertises a real frequency (3192MHz) that is inferior to the nominal base frequency (3200MHz), while it should be in turbo mode when running the viewer) ?...