4.1.0+ (July28) available Engine params.

[/Script/Engine.LocalPlayer]
AspectRatioAxisConstraint

[/Script/Engine.GarbageCollectionSettings]
r.Color.Max
r.Color.Min
r.Color.Mid
MinDesiredFrameRate
SmoothedFrameRateRange
gc.TimeBetweenPurgingPendingKillObjects
MaxPixelShaderAdditiveComplexityCount
MaxES2PixelShaderAdditiveComplexityCount
IdealLightMapDensity
MaxLightMapDensity
r.AmbientOcclusionLevels
r.AmbientOcclusionRadiusScale
r.AmbientOcclusionMaxQuality
r.AmbientOcclusionMipLevelFactor
r.AllowLandscapeShadows
r.EmitterSpawnRateScale
r.SeparateTranslucency
r.DistanceFieldShadowing
r.DistanceFieldAO
r.DefaultFeature.Bloom
r.DefaultFeature.AmbientOcclusion
r.DefaultFeature.AmbientOcclusionStaticFraction
r.DefaultFeature.MotionBlur
r.DefaultFeature.LensFlare
r.DefaultFeature.AntiAliasing
r.DetailMode
r.MipMapLODBias
r.MSAA.CompositingSampleCount
r.MaterialQualityLevel
r.SkeletalMeshLODBias
r.LightFunctionQuality
r.LensFlareQuality
r.LightShaftQuality
r.StaticMeshLODDistanceScale
r.SkeletalMeshLODRadiusScale
r.ShadowQuality
r.Shadow.CSM.MaxCascades
r.Shadow.CSM.TransitionScale
r.Shadow.MaxResolution
r.Shadow.RadiusThreshold
r.Shadow.DistanceScale
r.Streaming.MipBias
r.Streaming.PoolSize
r.Streaming.Boost
r.SSR.MaxRoughness
r.SSS.Scale
r.SSS.SampleSet
r.SSS.Quality
r.SSS.HalfRes
r.DepthOfFieldQuality
r.RenderTargetPoolMin
r.Upscale.Quality
r.MaxAnisotropy
r.EyeAdaptationQuality
r.FastBlurThreshold
r.ScreenPercentage
r.TranslucencyLightingVolumeDim
r.TranslucencyVolumeBlur
r.Tonemapper.GrainQuantization
r.TemporalAAFilterSize
r.TemporalAASharpness
r.TemporalAASamples
r.SceneColorFormat
r.SceneColorFringeQuality
r.ParticleLightQuality
r.ParticleMinTimeBetweenTicks
r.MinTimeBetweenTicks
r.PostProcessAAQuality
r.RefractionQuality
r.ViewDistanceScale
r.VolumetricFog
r.VolumetricFog.GridPixelSize
r.VolumetricFog.GridSizeZ
r.fog
foliage.CullAll
foliage.DitheredLOD
foliage.LODDistanceScale
foliage.MinLOD
foliage.OnlyLOD
foliage.DensityScale
grass.DensityScale
grass.MaxUpdateFrequency
BoostPlayerTextures
PerfIndexValues_ResolutionQuality