Can more memory than I need slow down my server?
I've not heard the terminology "extra wiring" but adding more ranks to a memory channel may slow it down. There should be documentation on the server that covers memory configurations, including what bus speed is supported with varying amounts of rank on each bus. It's pretty common for the speed to drop after about 3 to 4 ranks.
See also:
- DIMMs: Single vs. Double vs. Quad Rank
- SF Blog: Know Your RAM