I shall do some experimenting tonight with the lower speeds and post my findings (pics) - I've recently purchased a tripod, so the slower shutter speeds won't be a problem.
On a side note, picked up another prime lens 'bargain' today - Canon EF 28mm f/2.8 for just under $300, so my current lens selection is as follows:
Canon EF 28mm f/2.8
Canon EF 50mm f/1.8
Tamron SP Di II Macro 60mm f/2
Canon EF-S 18-55mm f/3.5-5.6
Canon EF-S 55-250mm f/4-5.6 (SOLD)