Particle beams are not really long range beams, they are always outclassed in the range group by standard lasers. They are more of a mid range beam and fit between things like rail guns and lasers, they are limited in how you can mount them, and thus their tracking speed though. You essentially slap them on the ship hull (think big pew pew out the nose cone), this means they are limited by two things. First your ship speed will give you a maximum tracking speed, but that can be reduced if your fire control tracking is lower. So if I have a ship moving at 5000 km/s but I can only design a tracking system capable of of 4000 km/s then the beam will be set at a tracking speed of 4000 km/s. This also works in reverse, so which ever is the lowest speed is what will set your beam tracking speed.
Where I find them useful though is how they outclass lasers at the top range of the particle beam, so they are nice big punchy beams at that range and as you start to get closer a laser becomes a better choice (of course the laser was best to begin with as it has a further reach too). How I tend to use Particle beams is on a very fast ship that I use more as a disabling weapon rather than destroying. When faced with an enemy that has large amounts of short range beams or things like mesons and other nasty stuff, I will chase them with my fast particle ships, but ensure I set an order so that my ship always stays just inside my particle range and never gets closer (this also works when being chased by someone), then I can happily sit an take potshots at them without fear of reprisal. Of course it involves lots of shouting at your tactical officer to stop hitting the reactors and start aiming for engines and such only.
I generally find them to be more of an RP thing though as there are few times when I can truly think "a particle beam is the only weapon for this task". More often than not I can happily use other weapons to achieve the same goal, and they have the advantage of other uses too.