FWIW, for a FUN, weekend car, the jz swap is fine. The pros are parts availability and the nearly double power output at a reasonable cost.
However, if its a daily driver which has to be reliable too, a m50 swap would be the best option. M52s are a bit tricky and are prone to nikasil and warpage issues if overheated. Although the 2.8 with a M50 2.5 manifold is a 230+ bhp contender!
Keep in mind, German power ratings are usually on the conservative side and BMWs perform better than other manufacturers' similarly rated cars.