As far as i can tell from using HDDs at that temp it really isn't a big problem.
A few years ago I used HDDs without fans and they were some of the first 7200RPM ones, i've also used SCSIs at 10K RPM and I never had any heat problems with the drives.
A while ago though I started using HDDs bays, you know the removable ones with fans and heatsinks. These dropped the temp of the HDDs considerably, but I have noticed no extra performance or reliability from the drives.
So if I were you I wouldn't worry about it.