Not a minute, but a noticeable time, especially if you have visuals running.

.wav files run about 6.5 times bigger than 192kbits/sec mp3s in my experience, so you'd need a cache 6.5 times as large to approximate the spin up frequency of 192kbits/s mp3s. Assuming that 12MB of a Mk2a is cache, then 82MB would be required. Of course, we know that a Mk2 runs happily with only 12MB total RAM, and indeed, a Mk1 only 8MB total RAM, so you should be able to beat their mp3 spin-up frequency with 64MB of RAM in a Mk2a playing .wavs.

But it's still not worth it IMO.