Well, DJ bikes are definitely designed for 80mm and 100mm of travel. You could probably do 120mm too, but any longer than that, and I'd say the bike geometry would start to feel kooky.
I run my circus at 120 and like it better than 100.
Circus have a much lower a2c than most other forks.
Usually about 15mm difference, so running a 120mm circus is comparable to running a +-105mm DJ / Argyle
Back to the question, don't exceed the maximum recommended length. It won't ride well the frame is not designed for the bigger steerer angle, so it's more likely to snap (also no warranty in this case). If you really want to and feel like it's still too low, don't push it more than 20mm over the maximum recommended length.
You can do a bit more tho when you have a Manitou or a Fox, as those forks have a lower a2c, so it takes more suspension to reach the same fork height.
I run my circus at 120 and like it better than 100.
Circus have a much lower a2c than most other forks.
Usually about 15mm difference, so running a 120mm circus is comparable to running a +-105mm DJ / Argyle
Back to the question, don't exceed the maximum recommended length. It won't ride well the frame is not designed for the bigger steerer angle, so it's more likely to snap (also no warranty in this case). If you really want to and feel like it's still too low, don't push it more than 20mm over the maximum recommended length.
You can do a bit more tho when you have a Manitou or a Fox, as those forks have a lower a2c, so it takes more suspension to reach the same fork height.