@WanaB
If you are prior service 18x you will still go through Infantry OSUT, but you will be given separate quarters, pass privileges, your phone, and be the platoon sergeant. You will more than likely jump into training at the start of white phase, or weapons qualification phase, and you will be required to pass and complete all the requirements of the other privates. You will learn the basics of land nav, and if you are lucky you will get experience on the red diamond course which will test you for sure.
If you go 11x, the above statement still applies, entirely. But you will be considered 11x, which still leaves you with options. Within the first 6 weeks of OSUT, you will have a chance to sign up for a Option 40 contract to goto airborne school then RASP. You should take that contract.
Sometime in weeks 8-11, a Special Forces Liaison will come and pull aside a very small group of individuals to offer 18x contracts too. I know this because I was one. Without going in with an 18x contract, to be considered you must have a 110+ GT score, 270 APFT, and qualify Expert in rifle marksmanship. The only way to get around not having a 270+ PT score would to have above like a 130 GT score and above a 240 PT score because you will be looked at as a potential 18D.
If you want to go the 11x route, you will be more than likely, but not one hundred percent, be given opportunities to go either Opt 40 or 18x, after you get a feel for what everything is like.
Worse case scenario, you goto the line and will more than likely have to finish your contract before you get another chance to goto SFAS>
Decent scenario, you go Option 40, make it through RASP, get Airborne and Ranger qualified, possibly some other high speed schools, and be a land nav machine ready to go to selection and make it through.
Best case scenario, you skip the utter bullshit you will have to go through to get to selection and go 18x. If you know you wanna end up there, as stated by others, just go 18x and get there. 18x is the golden ticket, you will get experience on the star course before you have to actually complete the star course, and you will be prepped more than the other guys. You will be in shape, and have fresh knowledge because of the extra courses you take.
BLUF: Probably take 18x if thats where you want to be.