EXECUTIVE SUMMARY: You'll get LESS "oomph" with 16/40, than with 15/45 (stock), 16/45 (popular choice), or certainly, 14/45, according to my calculations.
The 16/40 you propose multiplies torque far less than 15/45 (stock); considerably less than 14/45. The excessively high (low numerical) gear ratio likely could ultimately damage engine/bearings/etc. from excess lugging, especially when the bike is heavily weighted, seems to me.
Work the reciprocal division and compare the numbers. What does that mean? The reciprocal of 15/45 is 3.0; the final drive ratio of a stock KLR. The countershaft must rotate three times for the rear wheel to rotate once; the final drive ratio is 3.0. 14/45? Final drive ratio, about 3.2: countershaft sprocket must rotate 3.2 times for the rear wheel to rotate once. 16/40? Final drive ratio, 2.5--rear wheel rotates ever 2.5 countershaft revolutions.
Looking at a common mod, 16/45: Final drive ratio is about 2.8; yeah--rear wheel turns once in 2.8 countershaft revolutions. Your 16/40 2.5 drive ratio's pushing things, IMHO; suggest you check your calculator again.
One countershaft sprocket tooth corresponds to three rear sprocket teeth, considering stock gearing as a baseline.
DISCLAIMER: My postulations only; corrections, clarifications, and contrary opinions welcomed, as always!