I'd be getting it done sooner rather than later. As mentioned the inner joint wont wear as quick as the outer but as soon as the grease is out and the grit starts getting in its only a matter of time. Doesn't matter if your going to get a change over shaft of course but if yours is ok i'd be doing the boot rather than grabbing another shaft.
I killed an L series outer joint in a matter of weeks once, saw the boot was split but couldn't be arsed doing anything about it and within about 6 weeks it was clicking, I did live on a dirt road at the time though. That said I did a front outer on my gen2 in tassie a few years back and didnt fix it till i got back home a couple weeks later with no long lasting effects.
Id try and get it replaced in the next couple weeks if i was you, otherwise it will be chrissy/new year and that will be another couple weeks till mechanics are open again. Or DIY, the inner boot is about a five minute job (depending on how thoroughly you want clean out the joint) once the shaft is out. 
Had it looked at today, was quoted $95 to clean, re-grease, and replace the boot - said they have "special" ones now days that are are shaped a little different for the right hand side in an attempt to keep it away from the exhaust...
For a shaft change over they quoted me $250.
So just gonna do the boot - Wednesday morning - bout an hour they reckon (or they want to charge me for an hour regardless).
U will still have a massive gap with the normal lows but its up to u with which u choose.
My measuring suggests around 60-65mm clearance standard, the 28's are only gonna get rid of 30mm of it. Still gonna have 30-35mm gap.
Got the fronts the other day (28's). Took them out of the box and read the notice stuck to the plastic wrap. Special attention to no.4:
4. Check for Driver side and Passenger side (marked R/H or L/H on coil tag).
Only problem is - there is no damn coil tag or any R/H - L/H markings on the stupid things!!
Will have to consult them about this minor omission!
O/T: what year is your RX? My 1999 has the same headlights as your but different driving/fog light inserts. Looks like the same bumper/grill... I want ones that look like yours!!!