I found Windows 8 sometimes drops the wifi, but W7 did it too though not as bad.
You can try updating the wifi driver.
It seemed to help here, but still does it sometimes when I know the router is working as I can still be online with phone alongside. 
Not sure why it seems slow otherwise, have a look in task manager there may be some stuff running there you could turn off.
See what is using most of the CPU.
Is it slow even after a reboot?