The Sonata II is a decent case, and the power supply should be enough. You mean 450W right? I just got my friend that case with a Core2Duo system and it works just fine. You might need to get the optional front 120mm fan, and don't use the CPU exhaust manifold, but it'll keep your system decently cool. It looks pretty nice also.
I see you'd plan on tossing the junk PSU from a cheap case, but noted that it has a -5v rail that the Antec PSU lacks. Before you decide on a PSU check your mobo requirements. For example, my Abits still require that old -5V rail, which severely limits my choice of PSU. Despite the excellent reviews, and flawless performance of my systems (backup is similar), I would probably have chosen a different mobo if I'd known this. So far my Aspire PSUs are hanging in there fine...
MrsBytch, I will respectfully disagree with your comments about a cheap case, but one additional comment clears it up. Cheap cases are great, as long as airflow/cooling is adequate. I buy cheap cases too, but make sure the air path is decent and they have front and rear 120mm fan openings.
From the pics, it appears that the cheap Rosewell case has an opening for a 120mm fan in the rear, but comes with an 80mm fan. That will be louder and not work as well.
My next case will likely also include a top blowhole too, although I'm thinking of modding a case to add it, since my old Dremel still works.
If you are diligent in cleaning out your case on a regular basis filters are not important really. They "might" help muffle noise somewhat and are more for those who go a while without blowing out the case imo than anything.
Airflow of course will be a little better without the filters. As far as cases go the main things are:
1. Do you have enough room for what you're putting in it?
2. Is the airflow decent for the type/amount of cooling you plan to use?
3. Do you feel the case is aesthetically pleasing to you?
Thats about it!
I have an old decent atx case but it has no filters..
If you're considering keeping the old case I see no problem with that if it suits your cooling needs and looks good to you. If you need a new power supply however then I'd suggest just getting one of these new cases since you'd spend just as much JUST getting a decent power supply without the case.
On a side note I personally also like the Gigabyte/no power supply and the NZXT/w 400w power supply. The Antec Sonata II tho is a good case if you like its appearance. Solid power supply etc. Good choice. I know the two I linked have gotten very good reviews and good airflow plus I personally like something a bit of a different look but not too garrish.