For those of you that have moved to use the Salesforce Lightning Experience, or are looking too, you may find the below helps with any speed issues you may find.
Article to help with performance of Lightning Experience:
In your Org:
Setup > Session Settings > Click in the ‘Enable Content Delivery Network (CDN) for Lightning Component Framework’
We have had reports that once this checkbox is ticked, it does improve the usability of the solution, while working in Lightning. Some have reported an issue though with exporting of reports, so you may need to un-check the box if you experience this.