The difference between 3.27 and 3.45 is minimal and it's not worth the cost, unless you source VL diff gears and install them yourself.
A cam isn't such a good idea with a stock exhaust. The bottom line is I'd get some stock 14s for the moment - for use on private roads.
Also bear in mind any mods that might bring benefits in the short term could be incompatible with your longer term plans. You could get a 2.5" exhaust now, only to have to upgrade it to a 3" next year or something. This factor is the reason why so much of my car is still stock.