PhotoDemon provides a dedicated Gaussian Blur tool. Radii up to 500px are supported, and fractional radii are available for very specific blur strength. Three quality options are also provided; the difference between the three quality values is generally negligible, but the lower settings execute much faster (as much as 20x faster for very large radii).
Like all PhotoDemon tools, a dedicated command bar allows you to save and load custom presets, randomize parameters, and reset to default values. Last-used settings are automatically saved and restored, and all changes provide a real-time preview (no click or mouse button release required).