As for the Kemper pedals you only have one adjustment you can make and that is THRESHOLD. There are two gates available a 2:1 ratio and a 4:1 ratio. For metal you want 4:1 and keep pushing up the threshold until you get there. Clean tones you can use the 2:1 for a gentle cutoff.
There might be a gate adjustment on the input section but I would not mess with that since it will probably affect every rig.
I have played around with putting an EQ before the gate (usually the Graphic EQ). Then I set the HIGH CUT between 1.5 kHz and 7.5 kHz depending on the sound I am using.
The engineering formula to calculate noise includes BANDWIDTH. The narrower the bandwidth the less noise. So the high cut and any other cuts I do helps knock down a little bit of the noise.
I know nothing about IRs/Cabs but switching cabs sometimes helps cut some of the noise. Dont know why or how. It may just be filtering out a certain trouble frequency or cutting a lot of frequencies (reducing bandwidth). But it will also change the tone which you may not want.
There might be a gate adjustment on the input section but I would not mess with that since it will probably affect every rig.
The Gate Effects are fixed ratio/attack and release as you pointed out. They are simple gates and aren’t frequency conscious (they treat everything the same).
The gate in the input section is a totally different beast. It is an intelligent noise suppressor. Ideally it should remove noise before the reset of the signal chain and stop that noise being amplified (eq single coil pickup hum etc) without being noticeable so isn’t really suitable for tightening up palm mutes etc. It can be set for each individual guitar and made global by locking the input section or can be rig specific by not locking the input section.
Quote from Kemper ManualKNOISE GATE Knob (5)
This knob controls the Noise Gate, which eliminates the noise and hum of your guitar in a very smart way. Turn the NOISE GATE knob to the right until noise and hum have disappeared; do not turn it beyond that point, as this might alter the sound of your guitar. When set to the appropriate position, you will notice that noise and hum are eliminated, even when the strings are still sounding. There is no need for an additional release control as found in classic noise gates. The Noise Gate settings can be stored as part of a Rig.
Like "Clean Sens”, the Noise Gate setting is part of the Input Section and is stored with the Rig. It is also stored as part of any input preset. When the Input Section is locked, the noise gate is locked as well.
For metal sounds, we recommend adding one of the special noise gate effects, which are explained in the Noise Gate chapter.
Knoise gate?
It can be set for each individual guitar and made global by locking the input section or can be rig specific by not locking the input section.
Nice! I will have to give this a try.
Knoise gate?
It must be a Kemper thing. 
So pretty much I should just stick with the 4:1 and not even mess with the default input sections gate? I'll have to give those tricks a try!
I use both input and 4:1 pedal. My Input is locked and i use a small amount of gate to reduce hum. 4:1 to tight hi-gain chuging
