...is that one of the turbos is gubbed and my compression problem is due to failed valves.

 

so, options are:

 

replace the gubbed turbo with a standard new one;

replace both turbos with standard new ones;

replace both turbos with stage 1 new ones;

repalce both turbos with stage 2 new ones... :)

 

Car already has HKS EVC-IV boost controller and Central 20 ROM, if I go for Stage 2, what else might I need, and what likely power should I be looking at?

dont even think about only replacing 1 turbo, &

dont even think about replacing them with standard ones!! :)

 

down to you to decide the rest but injectors & IC's will be a minimum on stage 2 & higher.

Not relevant, but i did laugh when I saw you use the word GUBBED, havent heard that since I left glasgow

Are you not planning to run NOS too? If that is the case, you would be better off replacing both turbos with the hybrid ones Smithy has on offer, they'll be far better equipped to handle the increase over standards.