I you force master mode, your PC would be able to switch to 100 Mbps or disconnect. I don't think it affects LAN speed otherwise.
The settings that do affect speed are turning off any "Green Ethernet features", turning down Interrupt moderation, turn up buffers to a reasonable level, turn on jumbo frames, and turn off most packet "coalescing". There is an article on the main site about tuning those settings.
I hope this helps.
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