Without sawing off a 29" barrel it's hard to say for sure, but generally you can assume a difference of ~30fps per inch of barrel length change. So, chopping 5" off should give you ~150fps drop in MV. But, it could be as little as 50fps, or as much as 250fps. The 196gr bullets should see a larger change per inch than the 154gr bullets, but there's so many variables (bullet construction, powder type and charge, primer, twist rate, bore condition, etc) that it can be hard to predict.
And every caliber will be more sensitive to different variables. Just becuase a .243 has a certain rate of change means nothing when looking at the .260Rem even though they're both necked down .308 cartridges. Heck, even with the 8mm going from a Turk rifle to a Yugo carbine can introduce a whole lot more variables than just the shorter tube that it makes little sense to try to extrapolate how the barrel length change affected the performance.