Here's some test shots using the 1.4, 1.7 and 2x teleconverters - the subject being the mall sign. This gives you an idea of just how large of an image you can get with the teleconverters versus a bare-bones lens.
Bare-bones 70-200mm VRII
70-200 with 1.4x teleconverter (280mm)TC-14EII
70-200mm with 1.7x teleconverter (340mm)TC-17EII
70-200mm with 2.0x teleconverter (400mm)TC-20EIII
Another option for 400mm is the AF 80-400mm f/4.5-5.6 D ED VR though slower focussing.
...or the 70-300mm VR; both of which cannot take teleconverters.