Not much of one. There is little to no gain by switching up to a 90mm MAF when the car is NA. The stock MAF (80mm I believe for mach's to) works best for NA but if you were to SC it or turbo it you would see a noticable difference with a 90mm+ MAF.
The Maf will give you a nice gain, especialy coupled with an inlet pipe, be it C&L or your JLT. You don't need the 90mm but the 85mm C&L is about perfect IMHO. Plus the flow of the C&L is alot better than the stock one. Here are the C&L dyno charts with the inlet pipe and MAF. The peak HP and TQ differences aren't that much but look at the increase it gives you in other parts of the rpm range (much more important to me).