i also have the SL88 Studio, and i also had the same issue with the action: the heaviness can be improved a little by changing the curves, but it still feels slow and difficult to play, and much worse than (say) the Yamaha P-125. i believe the 73 and 88 Studio are just different sizes of the same action. if that's true, i definitely wouldn't recommend it; but there are people who really like it, so it might work for you...
i also wasn't particularly taken with the joystick controllers on the SL line. the short travel range and the way the two axes are connected made it awkward to adjust things on the fly.
i'm surprised we haven't heard anything about a refresh of these with the new TP/110 and TP/400 actions from the Numa x Piano range. the TP/110 in particular is supposed to be a lot better than the TP/100, based on a couple of reviews.