This doesn't answer your question but I thought I'd pass along some very important information that we just discovered last week.
If you choose the QSIG method, there are some hidden commands on the Nortel PBX that you'll want to turn on. By default, a call transfer will not trigger a QSIG Path Replacement proposal by the Meridian software. Depending on your network topology, this might leave up a lot of redundant call paths resulting in additional latency and multiple encodings.
The solution is an undocumented prompt in LD 17. There are two, actually: CTR1 and CTR2. They turn on path replacement messages for call transfers. Pick one and configure it on all of your Nortel PBXs that have QSIG connections on them. Don't try to mix them, though. Pick one of them and use it consistently.
John