I've had all of the big primes at one point or another, now I only have the 400/2.8 + TC's. But the lens I've been using the most is the Sigma 60-600...Thanks SK66 - not sure why I have this hankering for the 600 f4 when I already have the 400 2.8 and the TC14....
Something so special about these monsters I guess - plus severe GAS