Why only -5 ?
The camera can go around -30 ambient with air cooling only so you have lots of head room. I usually shoot between -16 and -20 during these winter nights. You will still get hot pixels but you will get a better response from your chip as regards signal to noise.
Go on ... crank up that fan. Manual recommends running at between 75-80% capacity from memory.
p.s. Image looks good.