You don't need SSDs. Raw 720p video at 24 bpp and 24 fps is 66 MB/sec, which a 5-year-old 7200 RPM HDD could serve.
66MB/s consistently is pushing it, and resolution, bpp and fps can all go substantially higher than the numbers you gave. More to the point, realistic systems could handle much higher resolutions (wherever the limit for that system was) using Lagarith than in raw.
In realistic cases something like Lagarith was traditionally worthwhile simply because you couldn't read raw video from disk fast enough. I don't know whether that's still true in the age of SSDs.