Information regarding boosted 4ag engines is very limited, almost to the extent of lack of experience,knowledge or individuals not disclosing information (black magic or dark art? I think not). When I started my project most turbo 4ag were utilizing t25/28 or in rare cases td04 wrx turbo. 98% of cases I researched were running stock valve train.
This made me broaden my research scope to a similar engine, the humble 4g63. Cam tests back to back was available including duration and lift. Most cases the springs were replaced with aftermarket items. This motion was highly supported by my tuner, largely because of valve float not seating under high boost conditions.
This was featured in my original tune where power dipped in the upper rev range but not due to turbo efficiency, lack of fuel or spark, or exhaust movement (choking).
I did have valve springs sitting on the shelf, but looking back at it I think I would have changed them in any case.