Retaining the 2.5L block means you keep the head drainage problem.
Also paying for all the machine work and sleeves and custom one-off parts is just insane. (Figure ~3-4 times the cost for a smaller displacement engine
)
I do not see the 3L block having "hot spots" on the cylinder walls either. Not with the casting process, material, and design.
If you want to go forged then I would run the 9:1 slugs (9.25-9.3 for you which is even better IMO!)
It sounds like your power goals are in the 400 range too so that is another big reason to get forged.
