Usually when I have had such a significant research lead, its b/c I found a nice indy site or free fort very early. The extra mage per turn tends to really snowball down the road. Did you find any great sites early on Z?
Utgard's main problem with not being able to stop Zeldor were 1) location - from now on I think I really want to only play wrap around maps and 2) the deadlock in the west with Arcos, LA Man, and Fomoria all having huge armies on my borders, forcing me into a defensive posture. None would agree to peace, yet never really attacked so it was a strange gridlock
Oh, and that early mass sneak attack by Eriu pretty much derailed any real threat Utgard could make. Never get too comfortable with the Sidhe as your neighbors!