Using the 440cc injectors may help; but I don’t think there is any assurance that they will work well.  Didn’t Rusty try this? 

 I don't remember it, but he may have. 

Yes, I tried the 440/460 injectors, and didn't see any improvement in idle.  If I'm not mistaken, Mazda rated these injectors at a lower than standard pressure.  For the guys who've had theirs tested, didn't they flow over 500 at standard pressure?  For some reason, I'm thinking that the 550's were rated at normal pressure, and RC Engineering tested 4 of mine with results between 549 and 551.  My thinking is that there isn't much difference between the stock injectors.

Mine tested at 570cc at 43 psi.

For idle, response time is more important, and I've always wondered if the difference wasn't between using high and low impedance injectors.

We put as scope on an injector lead a couple days ago.  We’re talking pulses on the order of a milisec at low power. I’d say those stock injectors just can’t react properly.

Al