about performance drops caused by STEAM and how mitigate them from my own experience this is what eats most CPU from highest to lowest 1. STEM friend-list (even while online, just closing friend-list saves most CPU usage) 2. STEAM chats (the more of them active the worse the overall load) 3. STEAM updating (as uses checksums it needs some CPU and I/O, so make sure nothing is updating) 4. STEAM overlay 5. STEAM IM (switch yourself to OFFLINE for lowest CPU usage) 6. STEAM website (if you keep website open and minimize, it still keeps playing the flash animations for example, so ideally you visit e.g. your profile page as last) + then set STEAM to lower priority than arma3.exe + Avast! antivirus users (but same rules can be used for other AV) shall read : http://forum.avast.com/index.php?topic=116952.0   +   this is what i use
```
"C:\Program Files (x86)\Steam\Steam.exe" -silent -nochatui -nofriendsui -console -no-browser
```
it allows run STEAMclient w/o new UI/chat/friends/popup/browser bloat
(especially those 200+ popups i can't disable about group/friends invites) it's very effective for fast testing (as someone who is game industry it's double important) for advanced gamer it saves some CPU / GPU cycles and some RAM /  VRAM space
even less stressing your SSD 
it avoids the STEAM browser cluttering the disk space with cache growing out of control when i want buy / discuss something i use reliable web browsers 
and when i want to join the chats/friends i just start it w/o those switches there are some more compatibility switches like
-complete_install_via_http
-tcp which may help in more firewall strict networked environment