Thankis for prompt reaction.
There may be indeed memory capacity problem, however test I have run in lower resolutions are undecisive.
Generally in 1024x768 glxgears (which I use as test vehicle) runs slower than in 1280x1024, but faster than 1400x1050.
Surprisingly, the 800x600 and 640x480 are not much better (only 30-40%) than 1024x768. This is kind of strange, considering the fact that this program runs pretty fast in 1400x1050 when launched in window of size 640x480.
Definitely, there may be something about lack of memory.
The question follows - can I do something to improve the situation (frame rate)?
Running at lower than native resolution on laptop's LCD is not feasible.