According to the specifications, you already have the highest performing CPU that the XPS 8910 supports. I think the Z170 chipset supports the i7-7700K which is a slight improvement but I don't believe the XPS 8910 BIOS has been updated to support that processor. 

@guthrie -  How much RAM do you have? Since the others said there's not much available to upgrade your i7 CPU, maybe more RAM and/or an SSD can improve performance...?

This PC has 4 DIMM slots and supports these (total) RAM configs: 8 GB, 16 GB, 24 GB, 32 and 64 GB using DDR4 RAM . Check the Specs for more details and have a look here for compatible RAM

Hi, @guthrie ,

I would certainly suggest that you look at the  suggestion, made by @RoHe , of replacing your HDD with a SSD! That would certainly boost performance!

@guthrie  - How much free space on those drives?

I guess you could go up to 64 GB of RAM, but probably not worth it...

How much junk is running in the background?

And sometimes, a totally clean install of Windows may help.

Good ideas, thanks.

Lots of stuff in background - as is windows typical. PerfMeter shows ~5% with user processes, another 15-18% with background processes - antiVirus, backup, and application junk that they all load!!

Performance is acceptable, but as always could be improved.

A clean rebuild is a good idea, but I have many-many things, and it would take 3-4 days to relocate, reinstall, reauthorize, reset options, etc. For all of that, I'll wait another year till I replace the system.

Have you scanned thoroughly for malware recently. Malwarebytes free version would be good.

Start by disabling as much background junk as you can on Startup tab in Task Manager, eg Adobe Reader Updater, Dell Update, SupportAssist, iTunes Helper, print managers, etc, if you have any of those. Just don't disable anything essential, like your antiviral app, audio and display items, etc.

You can also go to START>RUN>services.msc and disable (or set to Manual startup) things like Adobe Acrobat Update Service, any Apple services, Bonjour Service, xbox, fax, iPod service, etc. Again, don't disable anything essential and if you're not sure about something, don't change it's startup type...