What are you trying to achieve? Avoid hypens in domain names as much as possible. If you've got a forum relating to your consulting, I'd recommend YourMainDomain.com/forum or forum.YourMainDomain.com Dan
GDIForums Short and without hyphen. Avoid hyphens. Forum and Forums doesn't have big difference in search engine eye I think
Also GDIForums is two words gdiconsultingforum is three. A good rule of thumb is the less words the better.
This should be in the Domain Names forum. If you look, this area is called 'Buy, Sell and Trade', and I don't see any buying, selling or trading going on in this thread Click the report icon in the top right of your post and ask a mod to move it, or you could get infractions. BTW, I think GDIforums.com
GDIForums is better. In many countries, people won't speak "hyphen". Then they won't go to gdi-forum they will visit gdiforum and the last one is too much longer.
I don't think three words in the domain is bad, especially if they are good keywords. I experienced this myself with a two word domain that I changed to a three word domain. The site used to come up in searches for the two words. Now, it's on the first page of Google for the first two words, all three words, and is bouncing from #10 - #12 for the last two words. The third word I added is more competitive and was having a hard time ranking for it at all until it was in the domain name even though it was in the title, text, and description. So, if people are searching for gdi consulting, or gdi forum, you'll most likely rank higher for both with the domain name gdiconsultingforum(s). Relatively speaking, I agree that shorter domain names are better i.e. a three word domain is better than a five or six word domain but reduce it too much and you could be losing traffic.