DP, first, while the CPU's don't seem to be that much different, the new Intel i7 series is the latest, greatest from Intel.  You can read the Product Page from Intel's website.

Your computer only has 3GB of memory.  The e9180f has 9GB.  This may be overkill, but it is more than you will ever need.

The power supply unit (PSU) in the e9180f is 460W.  While I would rather see 600W, it is still about the best out there for prebuilt computers.

The GTS 250 video card has 1GB of memory.  This is four times that of your 8400GS 256MB.  This will add allot of performance.  Not to mention the advanecments that have been made since the 8400 series hit the market.

The sound will not make it any faster, but with 8 channel HD sound, it will sound a whole lot better.  Believe me.

IMHO, the only BIG downer in the e9180f is that it still has Vista installed.  I would rather see you buy a model that has already been upgraded to Win7.  I believe that you would be allot happier, also.

I hope this help with your decision.  Let me know if you have further questions.

I had already upgraded the ram on the m9040n to 8gig, video card to Diamond hd4650 1gig, as well as the power supply to 500watts, hard drive to 1.5tb and a blu-ray drive. I was wondering if I would see a performance increase when doing things such as video encoding. I also have an extra copy of Win 7 ultimate

if needed. Was just wondering if it was worth getting rid of the m9040n and upgrading to the e9180f?