Without getting into your debate about how 1 system compares with another, having only recently towered my A1200 with mediator etc (see sig), I can honestly say this is close to being a perfect Amiga. I can even switch it off using a mouse!
Having said that, it costs a lot to create it compared to a PC and you have to decide whether you want an Amiga or PC to do what you want.
But in general, any graphics card equipped miggy is far, far better than a stock one.
Check
www.Amigakit.com for prices; Matthew's service is brilliant and will help with knowledgeable advice.
