Long long ago (when I was a lot smarter) I wrote a few articles for the USHGA Hang Gliding Magazine about how ballast (and weight overall) affects your glide performance. They became available on Mark Forbes' Hang Gliding Magazine DVD's. They were just JPEG's on the DVD inside of the Adobe PDF format. Using Acrobat 8.0 I copied the pages from the articles and placed them up on the Oz Report web site (it's called repurposing) as JPEG's. They are accessible through thumbnails here.

These articles provide the background to a discussion of the effect of weight on glide performance. What we do know is that heavier pilots (like Attila and Balasz) have an advantage with a better glide ratio when going on glide, but perhaps a bit of a disadvantage when thermaling.

I looked at all the gliders and sizes shown in the previous articles and determined first which models would give me a wing loading of 2 pounds per square foot. The optimum wing loading proposed by the manufacturers was generally in the neighborhood of 1.8 pounds/square foot (it varied considerably), but I considered the optimum competition wing loading to be somewhat higher.

I then ranked the gliders that met this criteria by their span (in meters). They are as follows:

10.4 -Aero Combat L 13
10.3 - Moyes RS 3.5 (I need little ballast)
10.1 - Icaro Z9 13.2
10 - Moyes S 3.5 (I need a small amount of ballast)
10 - Airborne C4 - 13.5
9.8 - Wills Wing T2 - 144

So these are the gliders in span order than would give me 2 pounds/square foot. You would have to calculate which gliders would work for you and your hook in weight.

I then looked at which gliders I could fly and get 2 pounds/square foot if I added up to twenty pounds of ballast but no more than that (and often quite a bit less).  I then again ranked them by their span (in meters):

10.7 - Aeros Combat L 14
10.5 - Icaro Z9 14.1
10.4 - Moyes RS 4
10.4 - Moyes S 4.5
10.4 - Airborne C4 - 14
10.1 - Icaro Z9 13.7
10.2 - Wills Wing T2 - 154
10 - Moyes S 4

Have I done this correctly? Are spans comparable across these gliders?

Of course, these last three articles don't address the issue of climb rate and handling. Brett Hazlett writes:

But amongst similar designs span costs handling, so many choose to fly 'short' to enjoy flying more. Fair enough. The advantages of span are obvious on special days but mostly they are quite subtle. Still, this can be decisive in winning a competition. Handling, on the other hand, or rather the lack of handling is felt all damn day.

What to do about the handling issue is a matter of personal choice. You can go for ease with a short span but your performance will usually suffer to some degree unless you find ways to overcome the span effect with other effects. There are many. Generally, though, you should fly with as much span as you're willing to fly with. Going big with the span and having a ballast system is the most versatile.

Read both his articles here and here.