could you tell how much maximum data traffic (bandwidth) support to Router 750 in local LAN.

There's no strict number. It depends on the packet size, and what the router is doing to each packet. Is it tracking connections? Is it performing NAT? Is it changing packet headers, or running firewall rule sets against the packets?

The official number is in the datasheet on routerboard.com - but as I said above that number will heavily vary in production use depending on your configuration.

In my lan network 5/5Mbps data transfer in per second. it's works with in half an hour after that the router is going to hang and no access from telnet or winbox. after that reboot the router it's working fine. this process is doing every half an hour. so what the main problem???
is it high traffic capacity from router 750.

Again, that's impossible to tell without a lot more details.

Just pushing packets a 750 is going to handle 5/5 just fine, but if you have one thousand firewall rules inspecting every single packet it's not going to work well.

Do the router logs show anything when it hangs? If so, what? What's the CPU utilization at that time? What is your network layout and configuration?

the log says nothing coz it's disable. i have make a around 50/60 firewall rule as like web-proxy,particular port/website block. the cpu utilization is going to 92%.how can found the,which process is using the cpu.

If you are running 5.0 RCs you can use "/tool profile" to see what process uses resources.
If you're not, you're guessing. Could be a very unoptimized firewall rule set. Could be the proxy. The built in proxy isn't particularly great, particularly if you give it a lot of traffic to store on the slow internal NAND or flash storage - at that point the router is waiting for disk IO. Lots of proxy access rules can also slow down processing.

So as a first step maybe disable the proxy and all rules that forward traffic to it. Does that improve things?