Hm... not sure why you believe yor transactions would be slowed down too much but that's up to you.
Like with most other SQL DBMS you can prevent log writing, use temporary tables and different isolation levels to fine tune ACID compliance against performance.
In any case you should ensure you have a clear understanding of the exact requirements and implications of the chosen application design. (just sayin'...)
From your description I dont see why SAP HANA would not be a correct choice of platform.
- Lars