Hi Ominousplay

 Would you consider a last generation (or current) used MacPro from Craigslist? It will save you money- and be vastly faster than your eMac. I would go for the LED screen like the current iMacs have- GORGEOUS!!

I recently upgraded fromfour year old  pre-intel Mac G5 dual 2 Ghz to a current generation (used) Mac Pro 2.66 Ghz quad Xeon  "Nehalem". It was a really, really GOOD deal from Craigslist. I bought a 23 inch LED Samsung Monitor and the total was still less than the iMac 24 with the 3 Ghz Duo.(and much faster)

  LOVE the new iMac's btw, and I think the i7 version may outperform the Nehalem quad Xeon MacPro in some tasks- but I saved $1000 + with my set up. The Samsung LED monitor has that same amazing quality as the new iMac LED monitors. The "Nehalem" Xeon Quad is proving to perform much faster than I would expect just based on processor speed and number (4 vs 2) compared to my G5 dual 2 Ghz. The G5 twin Tower was already much faster than the eMac (my mother has one)- and my used (current Gen) Xeon MacPro is MUCH faster than the G5. Some of my test renders are TEN times faster-some 4 times faster.
 
 Personally- I do have a hesitancy to go ALL-IN-One since upgrades are limited. I have multiple internal hard drives, and I can swap out the graphics card if I desire- putting in more RAM is EASY and I can use 2nd party RAM (much cheaper).

    The MacPro line is expected to be updated with a new faster version of the Xeon processor in the next few months- and I am already seeing the current Nehalems on Craigslist.

   All that said- the i7 27 inch (LED) iMac is amazing- and would NOT be a wrong choice- I would go with at least 8 G RAM though, And YES paying the extra $300 for the i7 over the dual core would give you a much faster system. I would add att least one external HD for backup.If you don't want to go with used computers it is a fabulous choice since new MacPro desktops are more expensive.
After seeing the 27 inch screen iMac and playing with one at the APPLE store-I had a HARD time NOT pulling out my credit card!!! :-)

  If money was no object- I would have waited until the new Xeon (i9 like) MacPro's come out. They will outperform the i7 iMac.

 I spent months researching and considering alternatives, btw. And as a final word- if you do go used- make sure it has an Intel processor- I use several 3D apps- and one of them Vue 8 Infinite- is Intel only. I would not be surprised if Poser drops pre-Intel support at some time. The last non-intel macs came out 4 years ago.This spurred me to upgrade-or I would have plodded along with the 4 year old final gen G5.