Particle shields appear to be considered secondary in the order of importance for large ships compared to ray shields. For one they appear to be omni directional inhibitors stopping projectiles from all sides rather than the mono directional ray shield which only protected from outside attacks. This is shown in the hypervelocity gun. An HVG was a target during a simulated battle for a squadron of k-wings, several of which had been modified with a very large projectile ordinance. A heavily armored acclimator class cruiser drew the HVG's fire while the k-wings approached from low altitude (presumably to avoid detection) and began strafing the HVG as it fired. It was explained that every time the HVG fired an individual shell the particle shield was dropped for a split second to allow the shell to pass through and was raised immediately afterward. The projectile ordinance would hopefully manage to pass the shield area while the particle shield was down destroying the HVG very quickly. This was performed during the Black fleet crisis.

As for strength it primarly seems to be designed to stop micro meteors and explosions. A medium sized meteor was fired on by a star destroyer in Empire Strikes back for straying to close and a larger one impacted destroying the star destroyer almost instantly. A hyper velocity gun appears to be able to quickly deplete and penetrate the shields on even large ships. However a large number of explosives in syncronized fire appears to have a similar effect.

When rogue squadron attacks a star destroyer in their books they always tried to get their torpedoes to impact at the same time making the shields buckle. This could mean several things. The particle shields could recharge incredibly fast so that only a simultaneous detonation has enough punch to bring the shields down and overload the power or something (this also appears to bring down the ray shields, either through internal power overloads or fragmentation from the torpedoes impacts the shield generators (they appear delicate or prone to explosion from Return of the Jedi). Another possibility is that the particle shield merely detonates the warhead and the explosion energy is absorbed by the ray shields causing them to overload. As it appears that a large number of explosions in a small area has a devastating affect on both sets of shields this seems more likely to me. The reason that the explosion would be more dangerous than blaster fire to ray shielding is that it is coming from the inside of the shield or right inside of the shield compared to going into the shield (like an egg shell being broken from the inside).

Fighters do not appear to have particle shields instead relying on repulsion fields to protect against meteorites. X-wings all appear to have repulsors that enable vertical take off (Empire strikes back), and a set of tie bombers were equipped with high powered versions for use in an asteroid field by Lando Calrissian (I want to say it was in Vector Prime), a comment was made about making deflector shields extend beyond the hull of starships being a highly sought after technology which suggests a relationship of some kind between repulsors and particle shields.