Decay is generally a function of the diameter of a cymbal. Larger diameter cymbals have longer decay, smaller cymbals = shorter decay.
As far as the weight of the cymbal goes, it should match the dynamic at which the drummer plays, so if the drummer has a lighter touch, thinner cymbals are appropriate (larger diameter still has longer decay). If the guy is a neanderthal the cymbals should be heavier (larger diameter still has longer decay).
The ratio of crash/explosion to decay in a crash cymbal is similar for both heavy and thin models. The weight should fit the drummer's touch, and you, as engineer, set the mic's gain for the loudest expected dynamics, so the recorded crash:decay relationship remains rather similar between weights.
Other helpful tidbits about cymbal selection:
The larger a cymbal's diameter, the lower its pitch.
The thicker a cymbal is, the higher its pitch.
The flatter a cymbal's bow is, the lower its pitch.
The larger a cymbal's bell is, relative to overall diameter, the more complex its overtones.
Hand hammered cymbals (as opposed to machine hammered cymbals) tend to be have more complex overtones. Most hand hammering results in cymbals with a flatter profile and, therefore, lower pitch to go with those increased overtones.
LOTS of combinations available with these variables.
Last edited by Rascal Audio; 21st September 2012 at 01:36 AM..