I gotta say, I have never, ever seen a maxed out 4g63. Stock internals will take up to 600, and I doubt you know anyone that has done it.
A twin turbo inline would spool horribly. You would only have 2 cylinders spooling each turbo. Please understand a twin turbo first. Twin turbo on a inline 4 is a very stupid idea. It is almost absurd I am even reading this. Not trying to offend you, but I dont think you fully appreciate how expensive, and unefficent this would be. A single turbo setup would be far less, with more power.
As for the GT30, damn good turbo, but the 35r is actually more efficent in that housing, and it will actually spool as fast, or faster than a 30r. I would be happy to provide info to support this, as I know it may sound crazy.

 

the way i would split it would cause 100% of the air to flow through the k03 first.
but yea i know how expensive it is, im more into having one-off kinds of things than going fast. there was a reason my insurance used to be 2800 for liabilty lol.

and i know one person who had a 4g63 maxxed out, sick little old guy making 9's at Atco Raceway in a mirage i think it was, i really dont know how he kept it together, but his car was just a shell so i figured that it was neat he dropped the eingine in that small bay and our engines wont handle 600 on stock internals will they?

and actually i have already thought about a gt35 there is a company in lakeland, fl making complete kits for daily driving use, you porived the software you want or they will custom flash a chip, and they fab everything else for you, they are reporting spool times a little slower than a gt28 but way faster than a gt30. the only reason i havent jumped on it is cause of how cheap it is, it scares me, its not even close to 5 grand.

 

No offense to anyone for what I am about to say....
Well first, let me start off with this. I have been in the euro scene for quite some time, and have been around the euro crowd for quite some time. These cars offer me the most enjoyment, and I like the people that share the interest, and taste for these cars.
But:
Just because the kit isnt around 5k doesnt mean a damn thing lol. Some companies either just offer a fair price, or dont gouge because they dont have a huge name on it.
The kit shouldnt be around 5k..... Simple as that. No offense, but just because it isnt retardedly priced doesnt mean to really be weary. A GT35R is only 1500 bucks for the turbo.....
I guess the big name companies are damn good at what they do. Some people will pay any price to say they have a name on their car.