Upgrade the projector or projector screen?

Hello Everyone!
 My Current setup: 
Epson 5030ub + Screen Innovations series 3 - solar white (1.3 gain) 100 inch diagonal.

I sit about 8 feet away from the screen and my HT setup is totally dark with grey walls. 

My goal is to upgrade the picture quality and I want to stay under or around $5k. 

My QUESTION: Should I upgrade to a Stewart Filmscreen StudioTek130 screen OR upgrade my Projector to a JVC DLA x790r or similar? 

What will make the biggest positive impact? 

Upgrade the projector for sure!  The two screens you mentioned are pretty much almost the exact same thing.  Both white with 1.3 gain.  Both are very nice screens.  You are not going to get any difference with a new screen unless you drastically change the material (i.e. grey/black toned or super high gain).  Since you have a completely dark room, you're best result will actually be with the standard 1.3 gain screen.  Put your money into a much better projector.

You can also look at Sony projectors.  The JVC DLA projectors are noted to have very excellent black level and a film-like quality.  The Sony projectors are excellent as they make the image "pop" a lot more.  The Sony is a little bit more exciting but does not do as good in the lower blacks (shadow detail).

You can also look into a Lumagen Radiance video processor and then do a calibration.

I just went from Epson 5030ub to the Epson 6040ub. In my humble opinion the 6040ub has a better picture and I'm happy I changed. That being said, I'm a novice when it comes to projectors.
No doubt about it, upgrade the projector. For $5k you will be able to buy a used Sony 4k projector. I recently went from HD (Sony VPL-HW65ES ) to UHD/4k (Sony VPL-VW665ES). The difference in resolution and general image quality is staggering.
@auxinput: thanks for the advice. SI and Stewart are both 1.3 gain however I've seen Stewart studiotek screen and it is way smoother than my SI. That's why I wanted to know if swapping screens would make a big difference. Ive also heard from 2 different resellers that upgrading screen is more important. Have you ever A B'd screens with same projector? 

@ricred1 What screen do you have ?