A few updates.. Magically i just got it working realiably.
I disassembled the whole system, literally dish washed the motherboard, let it dry for a few days then reassembled everything trying out some new things.

Changed the power supply (again), cables, changed the VIO jumper on the motherboard from default 3.45v to 3.30v and changed the cpu jumper mode for jumperless (fsb, multis and voltage).
NOW im running it stable without CRC errors, at 2ghz (100x20) @1 .75v and memory at 133 (CAS 3).
I ´m not sure what fixed it, because i did a lot of changes in a row.

Installed Windows 98 SE, then Windows XP for a dual-boot. Everything working, EXCEPT for a huge performance difference between the OSes in 3D games and benchmarks.

In W98 SE using reference V3 drivers, with DX7 (tested with 8 also after) i´m getting 1473 3dmarks, Quake 2 in OpenGL barely hits 30 fps.
In WXP SP3 using Amigamerlin 2.5 drivers, with stock DX9 i´m getting 3700 3dmarks.

Using the same Via 4-in-1 chipset drivers in both OSes (4.43). V-SYNC is disabled, double checked.

Why is the V3 performing so poorly at W98??

Well, turns out it was the USB 2.0 controller card interfering in Windows 98 SE. Removing it fixed the performance: