A few points.
A dual core CPU will not actually be utilised fully unless the operating system and applications you are running support multi-core processors.
More often than not the advantage you will be getting is from the improved overall architecture and cache size that modorn CPUs have to offer.
Two cores certainly do not equal double performance, in fact far from it!
CPU clock speed is only one small link in a PC performance chain and is a clever marketing tool enabling PC stores to convince your Aunt Mabel that she really needs a 3 Gig PC to play bingo online.
Other key factors that can bottleneck the overall PCs performance are what size level 2 cache does the CPU have, what size is the memory, how fast does the memory run, what is the memory's timings, what speed front side bus does the motherboard run at, how fast is the hard drive.
Also, more importantly, why buy something that is out of date before you've even parted cash for it?
Although it's never a wise move to buy the absolute cutting edge of PC technology (you'll always pay a 30% premium for very little gain), it does make sense to try to go for uppper-mid to lower-high technology if you can somehow get the funds together.
Although there's no such thing as future proofing (as nobody knows what the future holds!), a higher spec setup will be useful for much longer and offer greater long term value for money.
One final question: Do you really need a laptop, how often are you going to be mobile? A desktop would offer considerably greater value for money. I know so many people who are squinting at tiny laptop screens and it never leaves their desk!
I hope the above helps you reach a decision!
