Old PC Upgrade Gateway FX6840-03e

[Jaceren]

Budget is a bit tight at the moment due to saving/paying off for a cruise for the wife and I in the fall. (Our first adult vacation. Yay!) Looking to upgrade this old PoS so it can at least run the newer games (Think Witcher 3 and Mass Effect: Andromeda) on the minimum settings. Focusing on the GPU (and PSU to handle it) as the CPU is somewhat decent. Will probably upgrade ram next month although I hear it's tricky on this model.

Full Specs Here: https://www.newegg.com/Product/Product.aspx?Item=N82E16883113135

Spec Rundown:
Intel Core i7 860 (2.8 GHz)
ATI Radeon HD 5750 (Such Poop)
8 GB DDR3 1333HZ

Plan on doing a completely new build (my first full build!) at some point next year so would preferably like to get a GPU that I would be happy with in a brand new build.

Budget is $300ish.

Was thinking something like...

http://pcpartpicker.com/product/7wgPxr/msi-radeon-rx-480-8gb-gaming-x-video-card-radeon-rx-480-gaming-x-8g

http://pcpartpicker.com/product/d8rcCJ/xfx-radeon-rx-480-8gb-xxx-oc-video-card-rx-480m8bfa6

http://pcpartpicker.com/product/7dJkcf/asus-radeon-rx-470-8gb-rog-strix-gaming-video-card-strix-rx470-o8g-gaming

My main issue is going to be space... (image of insides)
https://linustechtips.com/main/uploads/monthly_2016_02/E1C4302A-4A9B-430E-8C014691680539FA.jpg.6f57bdf2740642d048743101b1be52a9.jpg

What do you guys think?

Also what type of PSU does everyone suggest? Was thinking 750W. Is there any real reason I should go higher than that? My future build will be for gaming of course and I plan to put a pretty decent investment into it ($1000+ on top of what I buy now)

 

[imsqam]

I think that you have two choices, go for the RX 480 which is a decent GPU or blow the budget and get a GTX 1070. Here's one for 374 USD.
https://pcpartpicker.com/product/ph38TW/evga-geforce-gtx-1070-8gb-sc-gaming-video-card-08g-p4-5173-kr

The RX 480 is about the max that your CPU will allow without bottlenecking while the 1070 is more in-line with a $1300-$1400 build.

Your 500W bargain brand PSU will do for the time being, a quick calc finds you would likely be in the 400W range with the 480 installed.

Here is a tier list of PSU's although it is becoming somewhat dated. Once you find a particular model do a internet search for a review as you cannot depend on manufacturer only, need to look at the model. I use a lot of Seasonic, Corsair, EVGA, FSP and XFX PSU's in my builds.
http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html

If you need to purchase now with a new build in the future in mind, unless you are going to use dual GPU's or overclock, then a 550-650W is probably enough.