Path of Exile seems to perform poorly on ATI/AMD cards?

A week ago I upgraded my trusty old nVidia 8800GT to a brand-new spanking AMD Radeon HD7770. In most games the performance gain has been spectacular, I can even manage to squeeze out playable framerates in extremely demanding games like Battlefield 3 and Crysis 2. However, for some weird reason it's the other way around for Path of Exile! Whereas before I could run PoE pretty fluently on the 8800 GT with some details dialed down, it now performs downright poorly with the HD7770. Poor average framerates, lots of (sudden) framedrops, etc. I looked around a bit in this forum, and also asked around on the in-game general chat, and it seems that a lot (not exaggerating) of ATI/AMD card owners are experiencing similar problems! I figured it therefore would make sense to open a central topic for this problem here. ATI/AMD card owners unite! ;-)

So, what's going on GGG? Some kind of driver compatibility issue? Is this game even being tested on ATI/AMD cards? Could you please look into this?

P.S.: apart from this issue, I really like the game! Keep up the good work!

P.P.S.: I tried both the latest stable drivers and the latest beta drivers.

P.P.P.S.: Received the following reply from GGG:

"

We've received many reports of
problems with ATI cards, and there are a few responses scattered
through various threads that have been made. We have the cards on our
list to check and optimize for, but our lead programmer is still
dealing with the numerous problems caused by Open Beta so we likely
won't be able to investigate for at least a month, sorry! Any
information you can come up with for how well different driver
versions perform would be helpful, though we will of course do these
tests when we have copies of the cards in the office.

In http://www.pathofexile.com/forum/view-thread/83984 a lot of ATI/AMD card owners are reporting similar issues.

Seems like only the 5xxx/6xxx/7xxx ranges are affected, as I've heard from multiple 4xxx owners that they have no performance issues. So, driver issue?

Can't say I've had any strange FPS issues with my 7850 (13.2 Beta 4). I have the usual FPS stutter during new asset loading.

Hate to be brutal, I really like the game, but it runs like crap on my 7970, and I'm going to wait until something is done.

"

jantjeuh wrote:

Seems like only the 5xxx/6xxx/7xxx ranges are affected, as I've heard from multiple 4xxx owners that they have no performance issues. So, driver issue?

I use 4k series and I have this issue.

"

Espionage724 wrote:

Can't say I've had any strange FPS issues with my 7850 (13.2 Beta 4). I have the usual FPS stutter during new asset loading.

Same here 7870 reporting in A-OK

The only problem I have is v-sync gets stuck at 30fps, while my monitor is 120hz and the game plays at 200-300fps with it off.

Using a 7870 and the only problem I have is with AA. If I turn AA up to 8, my fps drops to 30. At AA:4 I get 160fps so it definitely seems odd. All the other settings seem to have no effect on FPS.

6670 here and I have the same issues, glad it isn't just my rig!

7970 reporting in - I get 250 fps unless it's in a full group with tons of spells going off, and then it's straight to shit.