Lukitoh,
I tried the CTK671, because their was so much hype about it, and the price was right for me also. I tried it on two occasions at two differnet stores and was not impressed at all. I don't understand the hype. I ended up buying a used PSR540. When I test a keyboard my main interest is the quality of the sounds, not the styles, not the effects. The Casio has a real synthesizer engine like the MS2000!! So what? No amount of tweaking a louzy sound is going to make it better. But I have faith in the quality of your ears, go ahead and try it for yourself, then go to the PSR550, PSR740, or PSR1000. Wouldn't it be better to go to the PSR1000 over the PSR740? If you can wait, hold out and see what the new Rolands will be like.
Starkeeper