Just a short performance report from my good old Vegas Pro setup...

System
CPU: Intel Xeon E5-2630V3 (8C/16T)
RAM: 64 GB RAM (Quad-Channel)
GPU: AMD RX480 - 8GB VRAM
OS: Windows 11 Pro
GPU-Driver: 21.30.23.01
HD: 2x 1 TB NVMe SSD (Samsung 970) / 3x 1 TB Samsung 860

Source Media from Canon Legria GX10

File(s) Size: 12GB (150 MBit) / 11 Files
Format/Codec: MP4/h.264
Resolution: 4K / 50 FPS UHD (Progressive)

Vegas Pro stock settings, except, uncheck both "Enable Legacy AVC-Decoding" and "Enable Legacy HEVC-Decoding".

Preview Performance
CPU: 13 - 15%
RAM: 8.5 / 64 GB

GPU: 40 - 50%
VRAM: 4.9 / 8 GB

GPU Video Decode: Max 60% (during crossfade)

Runs smooth like a moonwalk... even at crossfades!

Rendering Performance
Rendering Profile: Magix HEVC Internet UHD 2160p 50fps (AMD VCE)

CPU: 60 - 65%
RAM: 8.7 / 64 GB

GPU: 80 - 90%
VRAM: 3.0 / 8 GB

Rendering-Time: 17 Min 43 Sec (Playtime: 11 Min 30 Sec)
Output File-Size: 3.23 GB

Conclusion: There's no need for an expensive hardware upgrade. This machine still serves its purpose. I am happy =)