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#101
If it were my machine, I'd move up to 8.1 but the choice is yours. Win 8.1 has some pretty good reviews. I looked at Staples website and did not see Win7.
Operating Systems | Staples®
You'll probably get a better price online, shipping isn't bad - normally only a few days.
The following search results were sorted by TOTAL price - use that number to compare, not just the price (which doesn't include any shipping or tax)
Win 7 Home Premium (SP1): https://www.google.com/shopping/prod...6SQ#scoring:tp
Win 7 Professional (SP1) 64 bit: https://www.google.com/shopping/prod...6SQ#scoring:tp
Windows 8.1 64-bit https://www.google.com/shopping/prod...6SQ#scoring:tp