Mixing SFP's with different speeds
Solution 1:
If I installed Cisco GLC-SX-MM 1000Base SFP's, would that cause an issue if the other end of that fiber was connected to a 100Base SFP? Or do I need to have matching speeds on both ends?
Your speeds must match
Solution 2:
There are some handy links in this other serverfault question which might help.
How compatible are sfp's really?