First of all, if all you are doing is web surfing, emails and basic office work you don't need a powerful machine, or to pay a lot.
You certainly don't need 8Gb of memory, 4Gb is ample.
Also processor speed is not that import for most of the work you do, and processor speed will not affect download speed, he most important thing for that is your broadband speed.
You could have the most powerful computer in the world, but if your broadband speed is slow it wont download it any quicker.
I love Windows 7, but I HATE Windows 8. Microsoft sacked most of the key developers who created Windows 8 they were that disappointed with it.
I would either try to buy a machine with Windows 7 on it (not easy to do nowadays) or wait for windows 10 (but that is months away).
Some companies who make desktop PCs do allow you to select which version of Windows you want on it and offer Windows 7 so maybe go with one of them.