If you are going DiMarzio in a Mahogany guitar with floating trem, I guess the most tried, tested and popular choice would have to be Air Norton in Neck and Tone Zone in Bridge. Steve's Special is supposedly a brighter alternative for the bridge position.
If you choose the Seymour Duncan route, I guess Jazz/JB is most popular pick. Duncan Distortion seems favored too for the bridge.
If you are going EMGs, I would recommend staying off 85 in neck as it is too dark for an already bass heavy guitar.
81 goes well in neck and bridge. It has lots of bite and cuts through the mix well. It is amazingly tight for hi-gain rhythm but cleans suffer terribly.
60/60A is a winner for the neck. The cleans are amazing on these and has a nice bluesy lead tone too.
You could also try out the 89, 85TW etc if you need coil tap options and stuff.
I have used 81, 85 and 60 and I love the 81/60 currently in my guitar.
Let me know how it goes if you do make the switch. I'm looking at experimenting with DiMarzio/SD too.
-- My current rig
Guitar: '98 MIJ Ibanez RG520 QS w EMG 81/60
Amp: Laney LC15R Tube, Fernandes 20W SS
Pedals: MI Audio Tube Zone Overdrive, Boss OD3, CS3, MT2, HM2, DS2, CE5, DD7, TU3, Beta Aivin DD2 Delay, Dunlop Crybaby 95Q, Stranger Vol Pedal, BBE SupaCharger
Others: Yamaha RBX 374 Bass, Yamaha MM-6 Synth, M-Audio Fast Track, Shure SM-57, Heet Sound E-Bow Plus
Wanted(pm if selling): EB VPJr/Boss FV500L,Ibanez w Original/Lo-Pro Edge