[kalleboo]

I've understood it, the tradeoff is

The upside to variable length instructions is that they are on average shorter so you can fit more into your limited cache and you make better use of your RAM bandwidth.

The downside is that your decoder gets way more complex. By having a simpler decoder Apple instead has more of them (8 wide decode) and a big reorder buffer to keep them filled.

Supposedly Apple solved the downside by simply throwing lots of cache at the problem and putting the RAM on-chip.

I'm not a CPU guy and this is what I've gathered from various discussions so I'm happy to be corrected.