My first post here, but anyways. No you don't need to enable freesync to get that extra hertz, just put your screen to 75Hz (like I have) in your resolution settings in Windows and you are fine.
Freesync doesn't work with Nvidia (yet) so it really doesn't matter if you enable it or not, or am I wrong?
Anyways, back to the OP.
For that money Freesync is the only thing, you have to add a couple hundred more to get to the "good stuff".
There isn't much to go on with those specs, check for VA-panels maybe?
If you want IPS and 144Hz I'm pretty sure you need to go up to around 700-900 euros to get the g-sync monitors.
But if you can handle to get only 75Hz, then I would go for example the Ultrawide monitors at 2560x1080.
I bought an LG 29" Ultrawide 2560x1080 with IPS-panel, 75Hz and 5ms just a month ago. I love it, I'm never going back to 16:9!
Here are LGs ultrawide monitors, I guess other brands have the same line:
http://www.lg.com/us/ultrawide-monitors