Solved Unstable Broadcom/CAT5/Ethernet network speed. Is the driver buggy?

Friends on my Compaq DC7600 with a typical Broadcom ethernet controller, running Windows 8 Enterprise RTM 32-bit, the network performance is unreliable. With my windows 7 hdd in and running its flawless. If I still a USB wireless device in and run it to the same access point as is hosting the cabled connection, it is fast/furious. Sometimes the network link via CAT5 will start off with a blaze but then quickly drop to a crawl inside of 1sec.
Anyone seen this?

On ordinary internet traffic, flipping through web pages, it seems "normal" but the halt/herky/jerky disease triggers on any long-download item [such as a speedtest or a file download]

clues? Should I replace the default windows 8-installed driver with something else?

Have you tried shutting everything down - power off - leave for a few minutes and then power up.

I'd like some smarter folks than I to kick in an opinion or two.
since this problem, I pulled the drive and have been using ole' faithful Windows 7 which works just great. [also have terrible graphics/display/catalyst driver issues in 8]
anyway, got a new router for several reasons, set it up, works great on my Win7 thinkpad, hooked up the HP desktop again, plugged in and it worked terrific under Windows 7. did tests, big downloads, etc everything swell. Unhooked the win7 hdd, plugged up the win8 hdd, fired it up. When I first logged in, the network came alive and it stayed up for about 2 minutes or so, then went erratic, then lost Internet leg. Just to make sure it wasn't 3rd party security I disabled AVAST altogether. could not get the Internet leg back up.

I will try another driver on the nic and see if anything changes, but it sure smells like an error owing to the driver. I did not manually tweak anything as to the NIC's parameters.

EDIT: another question on the same: in Windows 8, perhaps for security reasons [?]: is the network link dormant until credentials are authenticated? is that the 'norm'? that is what I saw...

Broadcom NetXtreme NIC it turns out has a history of bad interaction of their 'FLOW CONTROL' feature in various windows iterations. Turned off [disabled] Flow Control and solved the problem. No more halts on larger downloads. No erratic net performance