Should I get a performance bike or an endurance bike for 180 km rides? I want to do the 180 km of cycling in general, that is the 2nd leg of Ironman.
I don't have a bicycle, as of now.
I am planning to buy a road bike (not the one used for triathlon).
People ask me to choose between a bike for endurance and a bike for performance.

I have ridden 200 km in a very cheap hybrid bike (twice the weight of an average road bike) in 11 hours.
I would be using the bike mainly for triathlons and long distance brevet(but brevets at a later stage), so mainly concentrating in tri.

Now my question is:
Doing 180 km in 6-7 hours come under race or endurance?
The speed involved here is 30 km/hr.
This will help me in choosing an endurance bike(Fuji, in my mind) or a performance bike (Trek, in my mind).
The terms "performance bike" and "endurance bike" aren't very well defined. To many people, the term "endurance bike" describes touring bicycles, which are used for long-distance self-supported rides where you're carrying a lot of equipment and supplies. However, Fuji (which you referred to), uses the term "endurance bike" to mean a road bike with a more relaxed geometry and "competition bike" to mean a road bike with more aggressive geometry. Trek (the other manufacturer you referred to), seems to use "sport bike" to refer to the relaxed geometry bikes, and "race performance bike" to refer to the aggressive geometry bikes.

The "endurance" and "competition" bikes are both high-performance road bikes, it's just that the "competition" bikes sacrifice a bit more comfort to eke out the highest possible performance (in theory, anyway). Most bike manufacturers have multiple product lines that cover both categories, so the general category of geometry doesn't necessarily dictate a decision between manufacturers.

I suspect that for the length of ride you're considering, you'll feel more comfortable on an relaxed geometry bike (e.g., "endurance" at Fuji or "sport" at Trek). But in the end, it's all about how you feel on the bike, so you should really test ride a few different bikes and see what you like best. No list of specifications, however long and detailed, can remove the need to try a bike and find out for yourself whether it works for you.