AFAIK, the XT530/531 are not very closely related to the XT3xx line. They mostly just seem to share cosmetic similarities with a different hardware platform.
Ignore what I just said, upon further inspection they do appear to be related, just based on the newer/faster msm7227T SOC.
Looks like I've got another device to add to my list.
Sent like a Streak of Light from Spidey, my Dell Streak 5
LG Optimus 2x P990HN (Tri Band UMTS, 1Ghz Dual Core Tegra 2, EuroSkank CM9) - my temporary main brain
Alcatel OT-909s "The Phone" (Dual Band UMTS, 600Mhz Qualcomm 7227, Stock Gingerbread) - my main phone
HTC Maple/Snap/Dash 3G "The Backup" (Dual Band UMTS, 528Mhz Qualcomm, Stock WM6.5) - semi-retired
Archos 80 Turbo - Coming Soon!