What driver version number are you using? Can you list the version that comes with windows 8.1? I am running windows 7x64 and tried the latest intel driver 17.0.0.34 and still have latency spikes on either the 2.4 or 5.2 ghz band when pinging my wireless router....
Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
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Reply from 192.168.1.1: bytes=32 time=2ms TTL=64
Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
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Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
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Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
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Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
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Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
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Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
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Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
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Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
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Reply from 192.168.1.1: bytes=32 time=1ms TTL=64
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Reply from 192.168.1.1: bytes=32 time=1ms TTL=64