Personally I wouldn't clip now, unless he has a full winter coat that is not shedding. It is so hard to get the coat healthy once you clip into the summer coat. It usually takes a couple of seasons to grow out again properly.
Put a bit of elbow grease in first, see if you can curry it all out of him. Furminators are great, and you can even use an old hand held vacuum to suck some of the loose hair out. The added benefit being the similar noise to clippers without the risk of cutting him if you slip ;)