About 18 months ago, I bought a HP laptop with a P4 2.80ghz for the amount of 1,300$ canadian dollars.
I added some RAM in it to make it even go faster. with a 15 inch widescreen display and close to 1 gig of RAM, it was not cheap nor very light weight: close to 8 pounds (3.5 kg).
My point is:
My laptop had a defective display hinge last month and I had to send it to service (under extended warranty). During this time, I had in my possession a "loaner" laptop that consisted in a Toshiba laptop model M-50: very light, 15 inch display, but cheap display, and very slowwwwww processor (Celeron). It couldn't even play DIVX compressed files without skipping frames. Its market price today: 895$ canadian dollars.
My conclusion:
In terms of laptop, you have two choices (after 15 years in this field I have seen hundreds of them): either you choose light weight, or power. Light weight can be slow and cheap or fast and very expensive. Heavier will bring you power for an average price (neither cheap or expensive).
So, choose according to your needs and remember that a few more pounds are very heavy when you have to carry it all the time. But if your laptop is meant to stay more at home, then weight does not really matter.
Hope that helps.
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Regards,
Benjilafouine