Most suspension corrected 29er frames untill recently, were designed for 80mm travel forks. The idea being to keep the front end from getting too high. Also with bigger tyres you need less travel. This has changed recently, with slacker head tubes, and more travel, seeping into the XC world. So a newer 29er frame is more likely to be 100m travel corrected. If you buy a 100/120mm travel 29er fork. You can usually limit them to 80mm anyway. Leaving the option for more travel and a slacker front end, if you want it (might handle poorly like that though, it difficult to predict).
You should be able to track down the hub-to-crown length, and rake, of you current fork, and compare it.
Most suspension corrected 29er frames untill recently, were designed for 80mm travel forks. The idea being to keep the front end from getting too high. Also with bigger tyres you need less travel. This has changed recently, with slacker head tubes, and more travel, seeping into the XC world. So a newer 29er frame is more likely to be 100m travel corrected. If you buy a 100/120mm travel 29er fork. You can usually limit them to 80mm anyway. Leaving the option for more travel and a slacker front end, if you want it (might handle poorly like that though, it difficult to predict).
You should be able to track down the hub-to-crown length, and rake, of you current fork, and compare it.