The GS is we know it is called the Aristo in Japan. All models are an Aristo so you cannot compare an Aristo to a Vertex.
There are two main variants the S300 and the V300.
The S300 is like the UK GS300 with the 2JZ-GE engine putting out around 220bhp.
The V300 is the twin turbo 2JZ-GTE engine putting out 280bhp (although probably nearer 300bhp).
Both the S300 and the V300 are available in standard form and the Vertex (some people incorrectly call it the Vortex). This is a higher spec model so you get a rear spoiler, HIDs, maybe bigger wheels etc. The V300 Vertex also gets active rear wheel steering.
The S300 is also available in Walnut Package which is like the Vertex model + wood trim interior.
Leather interior, sunroof and uprated stereos are options on all models.