Does having more RAM than my Windows edition supports impact performance?
Solution 1:
No, it will not affect performance. It only maps the amount of RAM that the particular edition supports, that's all.
Solution 2:
On modern hardware it will not affect performance at all.
There are exceptions, such as in the Pentium 1 era where some chipsets could not cache memory above 64MB (yes, megabyte, not gigabyte). I think it is safe to assume that you are running server 2008 on more modern hardware though. :)