Is suitable to run web proxy in transparent made with external cache on RB2011UiAS-2HnD-IN ?
when i tested start to run web proxy, memory is got lower than lower.
I wonder when memory is running out , will router board stop working ?
If have a way to run , explain me to how to configure?
Thanks 
For me web proxy with caching is totally un-usable any mikrotik routers, at least cheaper ones i tired, got HAP AC, and opening just single page like 9gag on single computer without any other traffic causes 100% CPU hit form proxy, same thing happens if you download things, at the end it slows web surfing and its counter-productive..
Thank for sharing experience-
How about if we run router os on virtual machine with two LAN ports?
Your better than with running squid proxy as it also caches HTTPS traffic, you wont get much benefits from Mikrotik one, but yes, it does work much better on more powerful hardware..
If you want a decent proxy with good cache that also has a nice feature called Update Accelerator, try IPFire on an x86 machine with minimum two nics.
Update Accelerator simplifies cache management for Windows updates, Linux updates as well as several other programs.
IPFire is a router distro OS.