I've solved my screen size issue using tightvncserver and 770x770 res as Qole proposed in different topic.
About performance - I assume that standard debian armel compilation doesn't make use of FP unit and so on.
Maybe some special libc would help as on 686 - optimised for our hardware but who could make one?
Mencoder runs 4times slower comparing per MHz with PIII system with SIMD opts.