NOT leased, I purchased it. As my tutorial clearly reads, if you're renting your unit, I wouldn't recommend messing with the hard drive.
The speed of the drive is largely irrelevant. Even if it was a 4200 RPM, it would more than likely have a transfer rate far in excess of what is needed to keep up with the HD data stream.
In the case of the drive I used, the Seagate ST9160310AS has a sustained internal transfer rate of 60.3 MB/s. Let's say, for argument's sake, that the HD PVR recorded data at the rate of a full high-def, 1080p movie - 6.75 MB/s (source: blu-ray.com). That would mean, that the Seagate hard drive has 10 TIMES the necessary speed to record the data rate associated with 1080p, and we all know that our PVRs don't do that anyway, so the actual data rate going to the hard drive is likely to be far less. Conclusion: the 5400 RPM drive is more than fast enough.
As for your comment about long-lasting, I'll put today's laptop drives up against full size drives any day. Why does Sony, for example, use laptop drives in their PS3s? I'll tell you why - Less heat, less power, and the reliability is just the same as a full size drive. But let's give you the benefit of the doubt on that one - let's say the Seagate falters in a year and half. I'd gladly spend the $73 to replace it than put up with the excruciating noise of the cheapo 3.5" drive that Motorola put in there.