I assumed I was running 480p, but having double-checked, it turns out I was running 525i. Try as I might, I couldn’t get the dash to enable 480p over SCART (I don’t know if that’s a limitation of RGB SCART or the Xbox?)
525i sounds right for PAL60 (NTSC frame size with PAL subcarrier, right?).
As I’ve understood it till now, PAL Xboxes only allow for PAL and PAL60, and you would need to use a softmod to change the video region to NTSC to gain access to 480p, 720p, and 1080i. This might not be correct if, as you’re suggesting, simply connecting a component cable lets you enable 480p; in that case, it sounds like the Xbox is indeed limited to 480i/576i over RGB SCART.
To make absolutely sure, I think we’d need to see how the Xbox behaves with the SCART cable and the video region set to NTSC.