Scrolling on Orion has a lot of stutters whether on 60Hz or 120Hz mode on most webpages.
The power consumption while scrolling is higher than Safari (24 watts vs 12 watts) on Youtube for reference.
Behavior happens on battery and on charger with a new Orion profile and compatibility mode.

Find below a comparison between :

Safari 26.4 (21624.1.16.11.4)
Orion RC 1.0.5 (144.1-rc), WebKit 625.1.8
On the latest macOS Tahoe 26.4.1 (25E253)
Using a MacBook Pro M4 16" (model Mac16,7) with 14 CPU cores (10 perf + 4 efficiency), 20 GPU cores and 24GB of shared memory.

The issue has always been there on Orion for me (user since about 2 years and Orion+ user since 1 year).

Steps to reproduce :

Download and launch the macmon utility (via homebrew or equivalent).
Open Safari 26.4
If not enabled, activate 120Hz rendering from the develop menu
Go to https://www.youtube.com/watch?v=npxlJdxSv4A
Set the video to theater mode and remove the subtitles, ambient mode, stable volume, voice boost, etc...
Let the video start then pause it. Scroll up and down quickly using the MacBook trackpad. Notice the smoothness and the total power consumption in macmon.
Create a new Orion profile then close the old one
From the Orion preferences, activate the rendering near 120Hz option
Go to https://www.youtube.com/watch?v=npxlJdxSv4A
From the Orion menu, enable compatibility mode then wait for the page to reload
Set the video to theater mode and remove the subtitles, ambient mode, stable volume, voice boost, etc...
Let the video start then pause it. Scroll up and down quickly using the MacBook trackpad. Notice the jittering and the total power consumption in macmon.

Video comparison :

Screen capture recorded at 120fps with BetterCapture then slowed down to 5% with iMovie.

Safari 26.4

Orion RC 1.0.5 (144.1-rc)

Notice the number of frames dropped while scrolling on Orion.
Notice the total power consumption reported (Safari = 12.68W vs Orion = 23.58W)

Timeline inspection comparison

Safari 26.4

Orion RC 1.0.5 (144.1-rc)

Analyze

Less CPU usage than Orion (67% vs 82%) and more usage of the main Thread.
Maximal duration of JS events is 8.8ms vs 155ms for Orion.
Same behavior for Layout & Rendering. Safari composite maximum duration is 9.938ms vs 21.90ms for Orion.
Orion has a lot of "full garbage collection" taking many miliseconds. Maybe a less optimized webkit than Safari ?

Activity monitor consumption

For the duration of the test (approximately the same time spent on Safari and Orion while scrolling on the same Youtube page), the power consuption is higher for Orion => Safari = 19.45 vs Orion = 29.45.

What was I expecting ?

Scroll as smooth as on the latest Safari Version 26.4 (21624.1.16.11.4).
Power consumption on par with Safari.

RC 1.0.5 (144.1-rc), WebKit 625.1.8

Tahoe (26)