If you're not doing heavy graphics or otherwise pressing the envelope, an i3 or i5 will be more than adequate to operate a laptop with one screen. Follow the advise of the sales guy. :-)
My laptop is an Acer Aspire 7745G with a Corsair solid state hard drive installed. CPU is an I7 720QM with 8 gigs of RAM and W7 64 bit. It has an ATI Radeon HD5650 video card in it and a 17.3" display.