There has been a huge improvement in the Garrett turbos since the GT series.
The GTX series provided a decent improvement by simply swapping in a milled compressor wheel. But the new (introduced about 5 years ago
) G series is a complete redesign improving both turbine and compressor efficiency by 15 to 20%. So you can now produce the same power with a much smaller sized turbo.
The compressor map for your GT3076 indicates a maximum flow of 53 lbs/minute (530 hp). The new G25-660 indicates a flow of 60 lbs/min (600hp) but is sized about the same as a GT/GTX2867r
So it would spool up a lot quicker than your GT3076r.
The G30-900 is the same size as your GT3076r but flows 820HP
Or maybe the G30-770 - it is similar size to a GT/GTX3071r but flows 700Hp.
An alternative would be the Borg Warner EFR7163. It flows 600Hp and is similar sized to a GT/GTX3071r, but because it has a ightweight titanium turbine wheel it would spool like a GTX2871
Obviously going with one of the higher flow turbos might require engine work, upgraded fuel system, a remap etc. Maybe you might be happy with the G25 or the EFR both of which would give a bit more power but much improved spool?