I don’t think the “4” makes the site seem less reputable … a bit less professional, maybe, but not to any great extent. Interesting that that’s your initial reaction, Focal. I wonder if anyone else has that same reaction?
If it’s in your budget, guljo, and since it seems that you’re already leaning toward this decision, I’d grab both domain names and have them direct to the same page. That way, if your site becomes successful in the future, you block the attempt to copycat it using the alternate domain.