Yes, I use Pureref. I used to have tons of folders with individual images, now I have one file for each project, which is super nice. I discovered the software almost a year ago and it made my work much more comfortable.
Thanks for the link, those concept arts are sick, I especially love the big bayonets, lots of cool stuff all around.
For your modeling project, it reminded me of an interview with George RR Martin, the writer of Game of Thrones, the interviewer asked him what he would do if he traveled back in time and was young again while retaining all his memories, he replied saying that he would freak out and wouldn't know if he could write all those books again, he was afraid he would mess them up.
It's normal to not be able to replicate your own work, in fact it's a good sign that you're making progress. Making progress doesn't always mean that your work is improving for the better, sometimes gaining new perspectives will make your results worse for a while. You need to let go of your need to do perfect work, and just have fun. If I were you I would look at the reference image once, put it aside, open Blender, and just model whatever crazy stuff my mind comes up with.
Trying to make a model that perfectly matches a reference image can be super stressful, you need to blow off some steam. What I did when starting out was for every hour spent on precision modeling, I do at least 15 minutes of freestyle wild crazy modeling, where I would take part of the model I made in the first hour, and just go to town on it, add weird things to it, try and turn it into a menacing spaceship, add cannons, spikes, and all sorts of crazy sh*t. It was fun, and I do it as often as I can.