A conventional flat like the Adidas Adizero Adios is a good choice for interval work on the track or grass.
I bought a pair of adidas adizero adios in 2012 and have done everything from 200m repeats to 5 mile races in them. I used the same pair for a 8 x400 workout several months ago. I feel like running some of my interval work in conventional shoes helps maintain my basic form and strength
Carbon Fiber shoes are probably a better choice if you are looking for a shoe for long tempos. They are just faster and easier on your legs, particularly over longer distances. For carbon fiber shoes, I would train in the same shoe you race in. If you have durability concerns, just buy two pairs.