So I tried your timings, but they lead to no sync at all when in text mode.
These settings work perfectly well on all my LCD PC monitors in text mode 720×400@70Hz as you can see on the first post of this thread, playing Doom (320×200) and Norton Commander (640×400).
I do not see any artifacts nor the corners cut off (no overscan).
Note that the resulting resolution will be 1152×864 (XGA+) with 384p Line2x which is in a VESA standard and works on all PC Monitors, but when not using Line2x the base 576×432 resolution is NOT part of the VESA standard.
You can raise H.Samplerate if you have overscan and recenter with Backporch and/or Synclength.
With 640×480@60Hz (320×240) modes, I see no artifacts nor overscan.
Note that when using upsample2x you should always use Line2x for 480p modes since upsampling requires higher resolution to not look jaggy.
Remember that using Line2x for 480p will output 960p, that PC monitors love, but TV’s hate.
What PC monitor are you using?