I already run 8 gauge through the speedo cable hole (don't ask... =)
But I'm a bit concerned that it's not up to the job of running 2 four channel amps (about 60-70 RMS watts a channel, about 480-560 in total )
If my sums are correct, 12 volts * 60 amps (the rating the cable came with) gives 720 Watts max.
I've been advised from a reputable dealer that you should only use up to about 2/3rds capacity, to allow for peaks (so 480 watts), which is a bit close really...

Coupled with the fact that routing the power wire to fit behind the speedo is a bit of a hack, I thought upgrading to 4 gauge cable and routing it properly was a good idea...

(Why am I running so many channels? Not for volume, but so it sounds nice... I used to run everything off one of the amps, but couldn't balance the front and the rear properly, hence the second amp to deal with the sub)

If any of the above sounds like a bunch of dingos kidneys, please feel free to correct me... =)

Jazz
(List 112, Mk2 12 gig #40. Mk1 4 gig #30. Mk3 1.6 16v)