It's not officially written anywhere, but given that they're (not quite perfectly, but close enough) copying National's program, where we have many years of experiences documented on FT, and based on some other reports here, anything larger than class C still allows you to pull from the Ultimate Choice areas (for your given status level).

That said, it seems an aberration that anything much nicer than an FCAR or a small SUV is in the UC area, so I certainly wouldn't expect to repeat your previous ORD experience very often...