Hey crim,
The fox pads I was talking about don't really provide much structual support for the knee they are more for impact protection. I also suffer a little bit of knee pain on longer rides but I got around that by using Rocktape under the pads to support the knee joint itself and it works a treat. I think anything more heavy duty like a full brace type system like mx'ers use would be to restrictive seeing as though we have to be able to pedal and they don't.
As for the g form pads, I myself perservered with them for about a month before they shit me to tears and I threw them away! I bought the recommended size for me and they fit great for about 2weeks and then became loose, I also had a medium paced stack in them and still lost bark off the knees, because they are so light weight and only held up by Lycra the second you slide in them they ride up or down your leg. Maybe good for the first point of impact but if your sliding, not so good (can you tell I ride in w.a pea gravel)
Anyway, good luck with you choice bud,
Cheers.