this remains to be seen. Most video processor (no matter if cheap or expensive) use unlocked output. This means the output is fixed to 50.00Hz PAL and 59.94Hz NTSC no matter what the input really is. Providing a semi-locked (XRGB-3) or 100% locked (XRGB-3 with vsync on) output is a risk and while VGA allowed for some flexibility HDMI is much more sensitive to non-standard video timings.You could get your scanlines from the XRGB-3 and then the zero lag upscaling to 1080p from the Flame Meister. Am I wrong in thinking this due to potential Hz issues?
I'm very happy with my TV performing the upscaling from 480p to 1080p and I wouldn't use another device in between, especially since the XRGB's B1 output isn't sharp enough to provide a base for pixel-perfect scaling as the XRGB does in B0 mode.