But if he's just trying to get a measure of how sharp different WAs are, using his standard zoom as a reference then you should be able to look up the numbers.
Here's the dpreview widget of the Sigma compared to the 18-55 VR:
http://www.dpreview.com/lensreviews/...on.xml%3F2
However I have a WA lens that is rated much better than either the Tamron or Sigma (Zuiko 9-18mm), yet subjectively I cannot tell any difference in sharpness compared to my kit lenses, mind you the oly kits are sharp too.
The main thing is a WA will get you shots you'll never get with a standard zoom - and any shot that is metered correctly, in focus, and steady, will be infinitely better than no shot at all, which is all you'll get with a standard zoom if it's not wide enough for the shot. To that point, any WA on a crop sensor is going to be good enough.