You can't get the large screens up to the same tensions as small. the frames start bowing because of the pressure. Most screen manufacturers publish tension guides. you get into the higher numbers, you will start ripping screens for no reason.
380 390 is used for detail printing with UV. the higher counts might become problematic getting enough ink down. cost starts to climb with weave. check out some of the new generation weaves, which feature thinner stronger threads - they provide for more mesh opening than the thicker thread standard stuff, and will take higher tension. Remember too, when it comes to mesh, it's just like cars - there are a number of manufacturers, and they have 'models' that range from 'Yaris' to 'Ferrari'. Most suppliers will always stock the cheapest shit they can find. there is a world of difference between some crap from china, and NBC/Murikami, or Sefar, or Saati. You get what yo pay for.
if you are having problems with blurring, yes up the tension to the mid 20's or higher if you can, but you need to look at your pressure/off contact. You might also try some of my friend Joe Clark's 'Smilin' Jack' blade - not sure of the price etc, but the design of the blade allows for way less pressure, higher speed and crisper prints. Clarke Product Renovation Tell him Andy sent you.