[andygold]

I'm looking to get a set of rails for my PS90, and a tac light to put on one of them. I'm seeing different slot amounts, extended, low profile, etc.

As I've never owned any weapons with rails before, I'm baffled by all the available options.

Other than the extended rails which seem to block the sight adjustment hole. (which i don't want), what is generally the best way to go? Any weapons light that will be put on the rail, at least for me, will be staying there, and not be taken on and off.

 

[CriticalDimensions]

There are many rails available to fit specific needs. A good variety are offered by Vendors here(see the links above) including Critical Dimensions.
The Extended Side Mount Accessory Rails we offer are extended in height not length. The extended height allows for easy slide-on & off of flashlights and laser accessories. With a PS90 the extended height is needed as the profile of the receiver prevents easy slide-on & off with low profile side mounts. The side mount accessory rails offered by FN have this extended height as well. If you're going to put it on for long terms, a low profile mount should meet your needs. Extra rail slots just give you those extra mounting positions, but not really needed in quantity on a PS90/P90 side rail mount.
Below is a pic of our Extended Side Mount Accessory Rails. We also offer other mounting rail options, just check the WTS & Critical Dimensions forums here.