XL/reinforced/Extraload can bare about 4 Li steps more load then Standard load. But need a bit higher pressure for the same load then SL.
This makes the sidewalls stiffer so lesser sideward sway.
Difference is small to my opinion .
But the extra reserve in loadcapacity is mostly nice.
So the advice pressures given on plate on car must be different , if extactly calculated by the car maker for GAWR.
But nowadays many car makers give for when towing rear pressure needed for maximum load called maxloadpressure ( SL 35 psi and XL// 41 psi) , or even maximum allowed cold pressure given on sidewall ( varying from 44 psi to 51 psi for SL and XL// sometimes up to 60 psi). And this is for instance for a Yeep with tires , of wich one can carry the whole Gross axle weight rating, to high, ( then XL is useless to step over to.
So then if you recalculate with my made extra save formula, then mayby you even get lower advice rear for XL .
So my advice is to let me calculate it for you , and I will give copy of text I used for other topics to show what info you need to give me for that.
Tirepressure advice is all about load on tire and speed ( and sometimes about alighnment - camber angle).
So if you can give details of car and tires , I can calculate an advice pressure with some reserve for things like, pressure-loss in time, unequall loading R/L, incidental extra load, misreadings of pressure scales,and misyudging of weight, etc.
This is from tires next and can be read from sidewall:
Maximum load or loadindex.
Kind of tire to determine the AT-pressure/pressure needed for the maximum load up to maximum speed of tire, or if lower 160km/99m/h/reference-pressure, wich is not the maximum pressure of tire.
Maximum speed of tire, most given as letter ( Q=160km/99m/h,N=140km/86m/h fi)
If you have offroad or tires looking like that , with large profile blocs that cover a part of sidewall, also mention, they are allowed lesser deflection then a normal road tire, then the tire maker used to determine the maximum load (to my conclusion the case for the Bridgestone tires on Ford Explorer in the Ford/Firestone affaire).
If you cant find all of it give sises of tire and Loadkind, then I will google for it.
From car next and mostly can be found on same plate as the original pressure advices:
GAWR and GVWR ( Gross Axle/Vehicle Weight Rating)
But best would be to determine the real weights in your use on seperate tires or estimate it as acurate as possible, by weighing per wheel(pair) or axle.
Maximum speed , you dont go over for even a minute in your use, eventually different for different situations, for instance when towing or fully loaded.This apart from trafic regulations, if you drive faster then allowed give that speed. Nature punnisches with tire-failure, police only with a penalty.
Give all that and I will calculate and give a picture of one of my filled in spreadsheets in my answer.
If other then original tires, indead as is already answered other advice is needed, a stiffer tire ( fi XL instead of Standard Load) needs a higher pressure for the same load, or the other way around, has lower loadcapacity for the same pressure.
Greatings from a Dutch pigheaded self-declared tire-pressure-specialist.