I think all the pros and cons of air to air versus water to air have been pretty well discussed in this thread, its not really a question of heat soak more efficiency, yes you could get a water to air chargecooler to achieve the same efficiency as an air to air but the complexity is the killer on an application such as the Supra that lends itself so well to air/air chargecooling, there really is nothing what so ever to be gained on the Supra by using water to air, you would be adding weight with all the extra components/coolant and an electric pump to deliver the water would be a head ache and require maintenance.
The only benefits i can see of the water/air chargecooler are where there are packaging issues (eg mid/rear engine) or running a power boat where you could use sea water to achieve near
100% efficiency