Which system are you saying is unstable, the A1200 or the Sam? I just recently installed OS4.1 on my A4000 and compared to OS4.0 it is considerably more stable. On a whole, I'd say my issues are more related to the amount of free memory than anything else and I'm playing around with a swap partition to see if that helps. On the A4000, NetSurf appears to be quite stable, ableit not as quick as I would like.
I can't speak to the Sam as I don't have one. Overall, I'm pretty impressed with how polished the installation is for OS4.1 for the classic machine. I'm typing this from NetSurf 2.8.
Adam