I have worked with most of the DS4XXX series of IBM (LSI rebranded really) and moving from one older model to the newer model is pretty straightforward.
So far, I have not been bitten nor had issues.
If you are using SVC, then the upgrade will really take just a point and a click - of course, the pre-work has to be done right!
One approach (assuming you are running AIX/Unix, well maybe later versions of Windows), and this is the most simple one to do (this assumes you are just moving away from the DS4500 on a one-to-one basis):
If you are doing it manually, you can:
1. zone the two togother,
2. size the VOL/LUN correctly on the DS4800 (matching what you have on the DS4500),
3. mirror the data from the DS4500 to the DS4800,
4. remove the DS4500 from the mirror,
5. unzone the DS4500 and
6. you're done! the DS4800 is now active!