I take it this isn't for DVD, and more likely for sending to a broadcaster. The specs given to you are more than manageble and within reason. The max bitrate of MPEG-2 really isn't limited as you suspect, but it seems to max out at around 160mbps for 1080p23.98. Of course, that bitrate is only for archival purposes, and there are quite a few houses that I know who encode SD for archive at 40-60mbps as well.
As far as a safe peak bitrate if you are encoding for DVD, I would say no more than 8.5mbps. I have seen some players that can handle up to 18mbps on the peak though. For broadcast, just encode at the max available specs you can, as it will be re-encoded once it is muxed into a transport stream and the bitrate is made significantly lower.
For encoding to really high bitrates and having total control over the encode, I would suggest the MainConcept Encoder. There are PC and Mac versions available.
Problem is, neither Compressor or Cleaner doesn't allow higher bitrates than 10 - 12 Mbit/s when encoding. We tried TMPGEnc -software as client suggested, but still no bitrates over 12 Mbit/s (plus it can't handle QuickTime video). Quality isn't really suitable for broadcast with these rates.
Is there a software that can do MPEG-2 with higher bitrates ?
As I said previously, the MainConcept Encoder will do this for you. ProCoder 2 is also capable of encoding MPEG-2 at higher bitrates. Both will accept QuickTimes. And, it should be noted that the content you are encoding will be broadcast at a much lower bitrate than what you provide to them. I would expect a 8mbps encode with Apple Compressor 2 to look pretty decent, but if all you have is Compressor 1 or Cleaner, then you may be trouble. A cheap app to try out on the mac is ffmpegX, although there are some caveats to its use.
And let me give a shout out to ProCoder as one of the highest quality and most flexible MPEG-2 tools out there. I've been doing the whackiest weird stuff with it lately, and the only thing it doesn't handle is transport streams with muxed ac-3.