I actually prefer 456, since it seems to keep better. I've had bleed-through problems with 499 (and yes, I store them tail-out). You can still hit just as hard, as well, and get nice, saturated harmonic distortion. For which tape variety has your machine been calibrated? If you can recalibrate yourself, try both under a variety of controlled situations. I'm lazy and unskilled, so I've stuck with 456 for a while and found it very satisfying.