Only a handful of people here have ever reported disk failure, and I don't recall any of those ever being definitely attributed to shock trauma. Statistically speaking, the empeg orientation works well. When you also consider that laptop drives are usually mounted horizontally in laptops, you also have to wonder whether the drive manufacturers take that into consideration when designing them to withstand g-forces.

I think that with rubber mounts and a laptop drive, you have probably cracked the problem though. If I were in your position I would probably mount the drive in whichever orientation worked the best in the space.