How do you know it only has the standard turbo? Could be a hi-flow. Could have an after market ECU. Does it have a standard exhaust, intercooler etc?
Time to do some poking around in the engine bay perhaps. Might find some more hidden treasure.
Aftermarket turbos rarely bolt straight on without manifold, wastegate and exhaust modifications, so if you're only chasing moderate power levels then a hi flow is perfect.
If you get something like Nistune installed, there's a fella on here called Toshi who does a really good job.
Can be done via Email. He will send you the files and you upload them to your ECU and bingo. There will be a bit of back and forth and some road testing but it's a damn site faster than snail mail.
Is 93 the highest octane fuel available there?
Mines the same also, dark face, -1 to +1 and i have an 02 model. And it's accurate. Although it's been replaced by the nismo triple gauge cluster now, as it didn't read high enough.