Did you try without the memory restriction after getting out of the first level? A couple people only had performance issues there, with the steam vent effect. Others have had this caused by anti-virus of firewall programs.
This is a little random, but maybe try the 4GB Patch to increase the amount of virtual memory that the game (or any 32 bit application) can access in 64 bit versions of Windows.

Try 1280x800. Zooming is only available in the resolutions where the width matches resolutions that the original disk version supported (ie in 1280x960 the text was a little too small on my monitor at the time, so I played at 1152x864, with a config file edit, and that disabled zooming; 1280x800 on my newer monitor in the download version of BD can zoom, though).

You should be able to adjust your build as you play; skills can be unlearned, and there aren't any stats that are useless to have a few points in.
The topic Killing Fergus has some early build advice, though you are past that point.
Alternately, check out the math appendix of the Beyond Divinity Strategy Guide.

There is no save editor for BD, just the manual Hex editing - gold, experience, stat/skill points
or Actiontrip.com's Beyond Divinity Cheats to start a new game with stronger characters.

For you cheaters out there (The Duplication Trick)

armory trick in act 1