So for set up:
GENERAL TAB
- better use vertical Pixel Order (is very accurate with estimate time)
- better turn OFF tonemap in Kray (so for that select LINEAR) and add BLENDING.
PHOTONS TAB
- the amount of photons is too small (I wrote the minimum is 1 million. Scene is small of course but better is to be sure all photons achieve corners)
- parameter N is too small. Minimum I suggest 600 but....in big scenes when you have a lot lights (physical and interpolated) will produce a lot splotches and errors and only high parameter N can reduce "hot/high colour" photons. DO not worry about contact shadow (parameter N reduce it) because we use extra Path Photons for corners and later QMC will calculate in these places very accurate GI. So parameter N for problematic scenes up to 3000!
- GI result ion is way to small. The best way is use Precomputed Unfiltered to see cells. It should be by visual feeling around 400 mm. I suggest 400 mm and I know is too big but...remember Path Tracing photons and QMC calculation. So even if GI is too high it will be secondary problem. Higher GI reduce bad cells information. Many times I used 300 mm but last time I noticed 400 mm has very good balance. Over or under make longer render also...
- do not use Pre cache blur.
FINAL GATHERING
When used QMC nothing works there (OFF parameters) except:
- FG min/max - the best setup (it means good balance quality/speed render) 50/300
After that De-noiser plugin in After Effect. The higher resolution then less visible noise.
- Path Passes - use maximum 1 bounce (over is longer time render and no visible better effect) + 75% Distance (Under appear light leaks , over longer render because amount of Path Tracing photons is bigger and is not necessary to use that far from corners because rest scene will be calculated by Interpolated photons)
SAMPLING TAB - very good

For higher resolution you can reduce strength of filter - it will be sharper, for example to 0.6. Box is very good and the fastest from all filters. Because Kray has problem with AA in small resolution (in your case 800 pix) better keep renders over 1000-1200 pix. But do not raise AA passes. G3 is maximum in my opinion. Of course with G4 will be a bit better but is not profitable (time speed render).
TONE MAP
- I suggest mix gamma with small amount exponential (for example Gamma 1.6/Exponential 4.0 with blending 80%) This I use last time non stop. Gamma will give you more accurate colours and small amount of Exponential will reduce a bit too strong light.
I do not use LWF...is too strong tone map and still I do not know how to deal with this property
