In the end it's about the dynamic compression; that is a function of static compression, valve timing, boost....
The common way is to trade static compression for boost to keep the same dynamic compression. Modern engines also use the valve timing to keep higher static compression off-boost.
One limit for your dynamic compression is that it will start to knock if you go too high. But that level will differ per engine. If you have a lot of back pressure from your manifold/turbo it will knock sooner that a high end manifold with big turbo.
The xu10j2te turbo is suitable and has been used before. It's not suited for really high boost/big bhp numbers but it is an easy conversion.
I would just try it.
Note that the turbo technics conversion for the 1.9 had a compression of 1:8.6 so you're not so far off..
Edited by wicked, 28 August 2017 - 10:38 AM.