Hi Jason22,
You can see most of the Optimum specs in post #48 here.
Probably yes … but it would depend on your area.
This would depend on whether the gel pad was cooler or warmer than the memory foam or latex you were putting it on top of. I would bear in mind that gel infused foams are not necessarily cooler than non gel infused foams. The gel is thermally conductive (like putting your hand on a countertop) which is a great selling tool because they can feel cooler when you put your hand on them but this doesn’t mean that they will be cooler over the course of the night because once temperatures equalize the foam will become an insulator. Long term “coolness” is more about ventilation and breathability and the ventilation of the foam that contains the gel is just as if not more important than the gel that is in it.
If you were to put gel memory foam on top of latex for example or above a quilting layer that had wool in it you would likely increase the sleeping temperature of the mattress.If you put it on top of memory foam that was less breathable then it may be cooler. You can read more about the different cooling technologies at the end of post #4 here and about the many factors that combine to influence sleeping temperature in post #2 here.
Some of the better options or possibilities I’m aware of in the St Louis area are listed in post #6 here.
You’re very welcome. After a day you probably know more of the “facts” behind mattresses and mattress materials than most of the people who sell them in the “mass market” stores. 
Phoenix