All your spell power gems convert to INT and you maintain about the same exact amount of spell power for them, its slightly greater than a 1/1 conversion. On my mage (mostly 264 with a few 277 pieces) I go for the socket bonus on gear that provides a +7 sp bonus, with SP/HASTE gems and SP/SPIRIT gems and just put in +23 spell power gems and skip anything with a +5 spell power bonus. Those have all changed to INT/SPIRIT and INT/HASTE, and as arcane seeing as im missing my 6% hit from talents, im going to have to pull out the old calculator and do some reforging/regemming for hit. Ill probably end up dumping spirit everywhere for hit at the reforger, and replacing the SP/SPIRIT gems for straight INT.
There is a lot of changes we havent seen yet, but I'm going to say along the lines of very similar to the way we gem now, except rather than stacking SP for red,SP/Haste or Crit for orange, SP/Spi for blue. Depending on which color Int is, i would stack as much as possible of it, it might lower our dps, but it will vastly increase both our mana pools and spell power.
Speccing something like this (very debateable, and not final):
And since all the cata talent calculators i know are down or glitched, no can do atm =/
i was wanting to mess around with runforging on the ptr but it seems it isnt on ... unless im looking in the wrong place ? where about is the runforger for horde. watched a vid on youtube and it seems to be beside the enchanter trainner in org. but it isnt there on ptr. as for talents havent messed around with them at all. altho i looked at the masterys and they seem sweet