I have OmniWeb/5.11.2/GM-v622.19.3 on 10.4.11/PPC, and that site doesn't cause me any problems.
Problem No1: cache rearrangement. If that site fetches lots of small files, and OmniWeb's disk cache is nearly out of space, OmniWeb can sometimes hang for 2-3 minutes while it prunes its disk cache. Are you familiar with Terminal.app? If you think this is happening, open Terminal.app and run "/usr/bin/sample OmniWeb 10" ... in the output, you should see lots of calls to WebKit code, and some to SQLite3. Fixes are (i) be patient and (ii) use the Flush Cache item on the main menu
Problem No2: ad blocking. If that site is fetching lots of banner ads, and many of them are Shockwave or Flash, OmniWeb doesn't really like that. If you're familiar with OmniWeb's Network Activity panel or Error Log window (menu items for these are on the Window menu) you could try working out from where the ads are being loaded, then use use Ad Blocking in Preferences to prevent them from being loaded.