Im new to the photography scene but i have a "Canon EF 75-300mm 1:4-5.6 ll" and i have had this lens for awhile and i noticed that they had a similar lens on the canon website that was listed as "Canon EF 75-300mm 1:4-5.6 III" and the only difference appears to be the II to III?? ... and both are ultrasonic...

are there any real big differences between the two.... im planning on shooting some sports photography ( sport bike racing ) and i wanted to make sure i was going out there with some good hardware.

thanks for any info !!