Joe – that’s a short cage by the look of things. I run an 11-32 cassette with a medium cage (GS) Ultegra R8000 mech on one bike and 11-28 with a short cage Ultegra 6800 on the other.
I don’t think you’d notice a huge difference between 105 and Ultegra for this part alone, but I do think it’s worth putting the small cost difference into perspective. You could easily save a lot more that the difference in cost between an Ultegra and 105 mech by paying more attention to how your pension / savings / mortgage / other costs are doing!
Life’s too short. If you want an Ultegra mech for another £15-20 over 105, just do it!