Quote - Here I made it less sharp. The render still took nine seconds. That shows that specular convolution is cheap.

Kerkythea's material system calls this feature "Specular Sampling". It samples a convolved copy of the environment sphere. It is not ray-tracing reflections.

Yes, but ... you used a kitchen counter.  Everyone knows that sampling from the kitchen counter is not allowed.

Lotus 123 ~ S-Render ~ OS/2 WARP ~ IBM 8088 / 4.77 Mhz ~ Hercules Ultima graphics, Hitachi 10 MB HDD, 64K RAM, 12 in diagonal CRT Monitor (16 colors / 60 Hz refresh rate), 240 Watt PS, Dual 1.44 MB Floppies, 2 button mouse input device.  Beige horizontal case.  I don't display my unit.