The clockport version is quite a bit slower than the Zorro version, but still quite usable. As for speed, an 030 can play back MP3s in 16-bit at low frequencies or bitrates, or with very the frequency division set very high. An 060 can play MP3s up to 128Kbps in 16-bit without cutting corners, and can manage 192Kbps if you drop the quality a bit. This is entirely dependent on the CPU, as the card doesn't have an on-board DSP.
OctaMED Sound Studio is a trickier proposition. An 030 or above can play MODs back in 16-bit sound, but you may have to drop the frequency a bit if the MOD has lots of channels. An 060 will play as many channels as you like, with effects turned on, at 44.1KHz+ without any problems.
However (and this is a big however), there seems to be a problem with either the board or its drivers (possibly the Toccata.library emulation?) when used with OctaMED. The board locks up after some use (the time before it locks up is inversely proportional to the amount of data OctaMED streams to it, so I'd imagine it's some sort of buffer overflow), freezing the machine and forcing you to reset it. This makes writing music with the card problematic and frustrating.
So, is it worth it? If you want to use it with OctaMED, I'd have to say no. It's far too frustrating to use, especially when you lose half an hour's work (it never runs for longer than that). For MP3 playback or 16-bit sample work, if you have an 060, it's not too bad. I think I'd probably recommend the Delfina instead, though you'd need to be aware of the problems with that card before you consider it (060 incompatible, buggy drivers, MP3 playback problems).