[SixOfSpades]

I would definitely favor a Gnomish Fighter/Illusionist over an Elven Fighter/Mage, but would have to say that a Cleric/Mage would beat out a Cleric/Illusionist.

For a Fighter/Illusionist, the main use of spells is to provide intense combat buffs, so the only spell you're missing is Spirit Armor--oh dear. A Cleric/Illusionist, on the other hand, is a mobile gunning turret, and the lack of Abi-Dhalzim's Horrid Wilting will really hurt their efficiency at their job.

Gnomes get better Saving Throws than Elves and Half-Elves, but that really applies only to Gnomish Fighters--so the Fighter/Illusionist would benefit from it, but the Cleric/Illusionist wouldn't notice much improvement. What they would notice is the -1 to Wisdom that Gnomes get, thus taking away from their Cleric side some of the extra spells they gained through their Illusionist side.