So I have now tested my WW2 loadout at the 3 main types of site (woodland, outdoor CQBish and indoor CQB). The 2 main issues are the weight and heat. The gear is a lot heavier than normal gear and the Sten is not a lightweight gun. The smock does get rather hot but is excellent in light rain. The webbing and clothing gives you a vast amount of carrying capacity. If I filled every part of a molle vest with pouches even over the back and then added a belt rig and drop leg's I might be able to carry almost as much.
The Sten: The range is decent but not exceptional, in woodland I wished I had a nice Lee Enfield to get some longer range shots in but it was doing better than some other AEG's. The Sten is noisy, the gearbox is fairly quiet but the piston seems to make one hell of a lot of noise so it's not a stealthy weapon. Outdoors the Sten excels at supressing enemies, the high rate of fire combined with the noise provides the shock and awe needed to stop a group of enemies and make then dive for cover. Equally if you want to cover someone then it draws attention away from team mates. Anytime you need to fire from a prone position, the Sten works well, the side mounted mag is excellent for this. In CQB it's not as good as my MP5 but I would rather have the Sten than an M4 or AK as the iron sights are really very good. Only the ability to have a torch or red dot sight would make M4's or AK's better. The Sten is sometimes impaired by the magazine position in CQB but equally the magazine position sometimes works in it's favour.
The Sten gun sling is a pain, especially in CQB and takes a lot of getting used to. I find that letting the sling slip down to my right elbow works. It's then possible to shoulder the gun quickly and easily and even switch hands.
My Sten chrono's at 335-338fps (10 shots semi auto) very consistent. Unfortunately that's technically to hot for the 328fps limit for the indoor site I use but they let me get away with it as long as I didn't do any head shots.