New imac or dell xps studio 8100/9000?

The new $1200 imac has intel i3 processor, 4GB RAM, 500 GB hard drive, and ATI radeon 4670 graphics card....The $1200 dell studio xps 8100/9000 has intel i7 processor, 8GB RAM, 1TB hard drive, and ATI radeon 5670 or 5770 for about the same price...Is it not straightforward that the dell would be better performance? I'm looking for a good computer primarily for making personal movie slideshows to pictures and video, etc. (like pics and videos of kids to music). I obviously like the looks of the imac better, but someone please justify to me why people would by the imac over this dell when the dell has much better specs? Thanks.