I noticed that in the mid temperature range, the heat display mode does not tell you very much. To increase resolution, in most thermal imaging, green is also used. This would give us a broader range (blue/light blue/green/yellow/red/white) (compare this picture: http://www.coldoneinc.com/Thermal%20Image%201.jpg).
What do you mean with lag? The difference between 'my' picture and yours is simply a different color range. Your suggested range looks better, I have to admit.
Changing the heat colour display will not increase lag at all. The reason I chose the current one was because it still shows particles that have no heat, I will do some tests with other displays before version 40 is released.