What should I do first - upgrade RAM or buy SSD?

Hello.

My current specs:

ASUS P8P67 Pro
Intel i5 2500K
6 Gb 1333 (2x1 + 2x2) RAM
ASUS GTX 560 Ti
HDD WD 320 Gb
El Capitan

I use this computer mostly for editing in Final Cut and After Effects.

What should I do first - upgrade RAM (buy 8/16/32 Gb 1600 RAM) or buy SSD (which will replace my HDD)?

Thank you.