I installed my RO system this weekend and I'm pretty excited. The water pressure seems low though. Not unbearably slow but much slower than before the system was put in. The system is 6 stage and has a dedicated faucet, a 3 gallon tank, and is all 1/4 plex tubing.
I have a conditioned crawlspace that stays within 5-10 degrees of my house. I put the unit in the crawlspace so i would still have room under my sink. (It's about 1.5-2 feet below the floor)
I installed in by cutting into a 1/2 pex (or cvpc?) pipe and using an adapter to change to the 1/4 inch pex. At the far end of the RO system I used a 2nd adapter to change back to the 1/2 inch to travel to the sink (it's about 4.5 feet). After it goes through the floor i used a 3rd adapter to change it one more time to 1/4 pex to match the faucet pipe.
The reason I kept the bigger pipe was in hopes that it could be considered as an additional "storage tank" in that that long run would hold more water than using a 1/4 pipe.