Bart,
I have one pair of Cocobolo grips on hand that are sanded and waiting to be checkered. Yes, the bordered grips are slightly thicker at the edges due to not being checkered, but not as thick as the Nill's.
Since I get the Nill grips smooth and they do not need to have the original checkering sanded off, they are somewhat thicker than the Cocobolo grips. In other words the "strongest" would be the bordered Nill ones. <img src="graemlins/yltype.gif" border="0" alt="[typing]" />