I’ve finally had the time to download and install ZendOptimizer and ZendGuard.

Both seem to work fine with ZenMagick and in particular in combination with core.php help speeding things up a lot.

I haven’t got any numbers to compare, but relative to running the store without any optimisation make up for perhaps 40% performance gain.

So, this might be time well spend invetigating PHP acceleration, unless your hosting provider does that already for you.