$tested_computers = @()
foreach ($computer in (Get-ADComputer -Filter '*' | Select -Expand Name))
{
    if(Test-Connection -Cn $computer -BufferSize 16 -Count 1 -ea 0 -quiet)
    {
        $tested_computers += $computer
    }
}

Get-WmiObject -ComputerName $tested_computers -Class Win32_NetworkAdapter | `
Where-Object { $_.Speed -ne $null -and $_.MACAddress -ne $null } | `
Format-Table -Property SystemName,Name,NetConnectionID,Speed