Hey Brian, I know you have been using a DeWalt 788 to cut your puzzles. Most 788's have a small amount of back to front movement that should still give you a 90° cut as long as you have good tension and yout table is at a perfect 90° to the blade. The quality control of the 788 has not been very good lately and some saws have way to much front to back movement than is acceptable. In fact in the class I taught this past weekend, they brought in a brand new saw off the floor that was over 1/16" off. We had a hard time controlling turns on this saw. So, if you buy another 788, check the blade travel before you take it home.
a small amount of front to back movement is desirable as it makes for a more agresive cut. The Excalibur saws have less front to back movement, so the cut is less aggressive than the DeWalt 788. There is an adjustment on the EX saws but not on the DeWalt saws. But the adjustment on the EX saws is tedious and cumbersome.
The new RBI saws by Buston have an easy adjustment on the blade clamps to adjust this movement. You can adjust from 0 movement for less agresive cuts to to a large degree of movement for a more aggressive cut.
So, you have to decide what you want, a more accurate cut or a more aggressive cut.