I'd like to point out that, from personal experience, the most important value of a long-run SC will be his encumberance and slottage. The Wyrm, while very powerful in a short engagement, which is the melee combat rankings are based on, with his encumberance of 4, will prove to be somewhat limp-wristed in an all out battle, particularly if you can't break the opposing army through Cause Fear. Many, many times I've had an SC fall not through loss of hitpoints, but because he passed out like a big sissy and lay there like a useless sack of potatoes until the opponent beat him to death. This has led to my conclusion that a quality SC should have a low or no encumberance. With an encumberance of 4, and 2 bites per round, your Wyrm's maximum kill potential is about 50 enemies before he passes out into the dirt. This will probably be less, because you'll lose fatigue from pre-battle buffing, and because your enemies are surely not likely to be so obliging as to always be hit, always die in the first hit, and always be gathered together in a single square that you can chomp on them with both of your bites. Not to mention that poison is time-release damage, which will likely lead to a lot of cases of "beating a dead horse", as your Wyrm chomps an opponent who's already doomed anyway.
It should also be noted that another disregarded factor in the melee ranking of a combat pretender chassis is the spells you actually buff yourself with, and the use of items. Your Wyrm's item selection is going to be rather limited. I'm guessing you plan on a Horror Helmet or two, and the Amulet of Resilience? Let me know how it goes, and if my prediction of the Wyrm passing out into the dirt from his encumberance rating comes true.
