Are you working locally or across a network? Why not large assembly mode, have you already tried it? Are the components complex parts? Do you only have the problem with this assembly?
Is there any way you could break it down to smaller sub-assemblies and do all your work there?
Unless the 360 components are very complex, that assy shouldn't warrant large assy mode.
What is the clock speed (GHz) of the Core i7 CPU.
Do you have other processes and add-ins running?
Can you run AssemblyXpert and post the results here?
Also run the Assembly Visualization tool and change the Mass column to SW-Rebuild Time to see which components are taking the most time.
EDIT: Is the performance OK after the assy is opened?
What is the image quality setting in your files?