In Norway we have a huge forum called "Diskusjon.no" which means "Discussion.no". It is divided into almost every genre like "Hardware", "Games", "Companies", "Cars", "Boating", "Leisure", "Jobs and Education", "Culture", "Audio", "Mobile phones", "Workout" etc. You get the point.
Anyways, this is Norway's biggest and most popular forum and it has got several hundred thousand members with several thousand posts daily. This is a lot for a small country like Norway.
So, my point is, I could see Forums dot com be developed into something similar. It could be the biggest forum on the internet, in every genre.
So yes, it's an amazing category killer and it's definitely the best in it's genre (the singular would also be great), but I think you will have to wait long for a 7 figure offer, as a potential "end-user" wouldn't have such funds. If it was Banks.com, Loans.com or Cars.com then the sky wouldn't even be the limit of what you could expect, as your potential buyers would be extremely well funded. Anywhere near low-mid $xxx,xxx would be a great sale and I would definitely be happy with it without thinking "I could get more if I waited longer".
It's an amazing name, so good luck with it and I hope it will make you a fortune.
*2 cents paid at the counter.*