DVD Architect is famous (or is that infamous??) for incorrectly reporting file sizes.
Check the actual file sizes of the MPEG-2 & AC-3 streams that you rendered and, if they’re under the 4.3 GB limit, ignore the warning and render.
BTW, my bitrate calculator gives a CBR of 6300 or a VBR of 7800/6300/3700.
If your numbers are close to that, once again, ignore the warning.