Most impactful hardware upgrade

Hello fellow gear heads,

I have some 15 years of experience in the IT field, so I have a good understanding of what I'm talking about... But my time on Premiere is much more limited 

The video I'm working with is not complicated, a few 10 or so minute clips from a pair of Canon camcorders totalling 30-40 minutes of teaching by a pastor at our church... A bit of color correction, some lower thirds and motion graphics templates and a pre-rendered open/close sequence from After Effects.

I have to use software rendering or the preview rendering process craps out.

I'm looking for input as to what is the first, best thing to do to improve performance for previewing and encoding/exporting.

Current spec:

4th Gen i7 6 core @ 2.9 ghz

64gb ddr3 ram

Sata 3 SSDs

GeForce 750TI 2gb

I didn't buy / build this machine  I... Uh... Inherited it, originally intended for hosting VMs as a testbed.

I'm thinking the first, best upgrade will be a newer video card, I'm looking at either a GeForce 1050 4gb or a 1060 3gb card.

I plan on upgrading the whole thing but I just don't have $1000 to do it all at once. 

Thoughts / comments?