I'm close to purchasing a Motordyne 5/16 spacer, but I see there is a basic, iso-thermal, and copper iso-thermal.

I was almost going to purchase the basic until I noticed the other two. Is there any big benefit to paying a bit more and getting the iso-thermal/copper iso-thermal?

 

The iso-thermal will add the aramid gasket (goes between the upper and lower plenum) which will lower heat soak, and it also comes with the coolant bypass valve which will allow you to shut off TB warming from the coolant during the summer...thereby reducing heat soak as well.

The copper iso-thermal comes with a copper throttle body gasket that will do the same thing as the coolant bypass valve except you won't have to remember to shut the valve off in cold weather where its vital to the TB function. It also comes with the aramid gasket.