Dell Optiplex 745 System upgrade to i5-4xxx

[UETIAN]

Hi all,
I have a very old Dell Optiplex 745 with Intel Core 2 Duo E6300, and 4GB RAM.
I intend to upgrade this system. The CPU, Motherboard and RAM will be definitely changed.
Core 2 Duo E6300 was a 65W CPU, while i5-4570 is 84W CPU, other than this I don't know if any component (e.g. MB) will cause power consumption change.
So the question is:
Is it wise to change only CPU+RAM+MB while keeping rest of the system unchanged?
The reason: I am sure the CD/DVD drive and casing etc., are doing well at the moment, so no need to waste money on those components.

 

[Dark Lord of Tech]

You will need a HASWELL compatible PSU also , and a new case , time for a whole new build.

 

[dwatterworth]

I wouldn't put too much into upgrading the system. I have a bunch of these Dell 745 and 755's kicking around the office. The Dell motherboards and cases were a BTX form factor, which is not compatible with any modern aftermarket motherboards. Also, the PSU will not be able to reliably power a new motherboard, not to mention in Dells cost cutting methods, the power cables are ridiculously short and would need at least 6" extensions. Also, those power supplies cannot come close to hitting any of the C-states that haswell chips need, you might run into instability even with the C states disabled on the motherboard bios.

The PSU in addition, is a strange form factor and will not work in new cases, there is about a 8mm extension on the side opposite the internal fan grill.

I would just keep that system as is for an internet browsing machine or something of that sort.
Build a completely new system, you can save $20 by re-using the DVD drive, but past that, nothing would be compatible.