What you did is fine..but is really only a bandaid...First you ran a new wire to battery from alternator..well..the old wiring that runs to the ECU and other electronics..still has the same resistance or problem that was causing the .5 drop. Did you measure the voltage at the fuse block..inside the car...bet there is still a drop....You measured your voltage at the battery and the amp..which is all new wiring...not 18 year old wiring. Also your 90 amp alternator..is not 90 amps...you lose 10amps at idle..if your 45amp charge theory...is even correct up to 18 amps at full output...once the case gets hot...Oh..and you can't compare or justify what you did to adding or being a benefit over a hi amp alternator...not even close..y Also your amp is nowhere near 1700 watts..lol..the actual wattage is the amperage times voltage...not the fuse rating!!! The amperage it's drawing while playing at max volume with no distortion..you'll need an ampmeter to measure that...I'm betting that with the stereo pumping..the headlights...the a/c...your alternator is struggling to keep up.
So I'm having this dream! I'm in my Z and these guys are after me, but they can't catch me...So they get a car, but they still can't catch me. So they get a plane, and just as their about to catch me....the TWIN TURBOS KICK IN!