most of this stuff could be searched, but i'm feeling nice today.
stock SR revs to 7500rpm, stock turbo on stock boost (7psi) runs out of breath a bit up there, but turning the boost up will solve that somewhat
don't worry about the speedo, if you're running out of room you're gonna get arrested anyway
if you really need to know speed that high, just remember you're revs and what gear you were in and do some simple math or find an internet gear ratio spreadsheet/converter.
as far as gauges, for an S14 you can probably just get an S14 gauge cluster or tach, or (gasp, please don't) get a ricey gigantic tach.
don't forget boost gauge! EGT and oil pressure wouldn't be a bad idea... i'm swapping a '92 and i've already gotten the boost gauge, and plan on getting the EGT by next month...