The maximum size you can import is really depending on two factors, #1 the requestLimits set, and #2 your network. The latter is not something which you can really set, some packages are just too large to be handled in a reasonable way over some networks. This should not be a problem if your network is setup correctly, so lets focus on #1 for now.
You mention you want to upload a package of 950 MB, and you have set the
maxAllowedContentLength to 200 MB, which means you specify in IIS that you will not allow anything larger than 200 MB, so indeed your Content Porter package of 950 MB is too large and will be denied.
Try setting the following in your
This will allow for packages of 2 GB to be uploaded (so your 950 MB should be fine), please note that depending on your network, it might be slow as the packages get larger.