> "User request no delay for this transaction"
As you've said there is always a delay somewhere and if you've got SAN you've got little control over it.
> So If I change all primary key as non-cluster, should have improvement for this transaction, right?
Not necessarily. "The best thing to do is test"
If you're inserting one row at a time in sequence - I see no reason not to use a clustered index (saves space and in the world of SANs smaller space = better performance). If the row is quite small then you'd only get a page split every once in a while. But, if you're inserting one row at a time then you're obviously not a high-performance system anyway so it doesn't really matter if the index is a clustered one or a non-clustered one.
I'd focus on what you do with the data afterwards. Most systems are write-once read many so the emphasis is on fast selects where clustering really helps. However, since you're using sequential id's as your key rather than a logical PK then I doubt clustering will help you. Personally I don't use sequential id's as a primary key.