Worthwhile lens upgrade?

[onyx39]

Currently have an Eos450d, which I upgraded from a 300d (massive improvement)', bought a used Canon fit 75-300 lens to replace a previous lens, now looking at the shorter focal length.
Is this a worthwhile upgrade from the standard kits lens?
I realise that being a 2.8 aperture as opposed to 4.5, but are there other benefits!