Its actually mmHG not psi when you are talking about the negative units on your boost guage. You can't really have negative pounds per square inch if you think about it.
But yeah mine sits on ~ -20 on idle.
When you did the comp tests were they just generally low numbers or was there lots of variance? Because if its been sitting for ages its quite likely it will be down.
What's the point if you are going to buy a GTR? put the money towards the GTR, you'll have it sooner and probably able to buy something already built saving you even more money in the end.
Get a remap, I bet its running way to rich. That was the cause of mine and alot of other misfires. The ultra rich condition often brings the worn coil packs to their knees hence new coil packs/plugs fixing the issue.
Revving in neutral doesn't really show much, really gotta do a drive by as its always going to sound different under load. Personally I've never really heard any NA rb's that sound nice, most have a horrible rasp to them.
Lots of cars run with no bov, search for 'flutter' and read the countless threads arguing about not running a bov. Its not going to do any harm if you are running basically standard boost.