sysadmin here. Greg F has nailed it.
First, 5 Mbps is not your problem, you should have plenty of throughput available for that. Check that your provider is not limiting your bandwidth, change providers if necessary.
Second, the raid. Software raid won't get the job done, especially when it comes to recovery (speed takes a hit too). The array must be hardware controlled and even then you have to be careful that the raid card is legit. Even then, you have to be careful. Sometimes a server will come with 'built-in' hardware raid which is in fact raid software that runs from the BIOS. That's what we call 'fakeraid' and it is garbage. The array MUST BE HARDWARE RAID, accept no substitutions.