AFAICR what you've said is 100% correct on this model. I made a mental note the other day to check at work if Compaq parts belonging to another geography might facilitate a worthwhile upgrade to what I assume is a US A7400 model (but forgot!) - I'd assume you've already looked in the QRG that I would use too but there's no harm double checking. If I find anything I'll report back here tomorrow but I don't see anything changing beyond what's been said here already.
Add to that, even if there is something that will yield a substantially better performance it's probably going to cost an arm and a leg anyhow