I would not recommend using both high bitrate and 2-pass encoding together. The purpose of 2-pass encoding is to estimate and assign more bits for high complexity scenes which need them at the expense of more simple ones. So the bitrate 1024 you mentioned above is an average bitrate value (with local maximums and minimums far away from this value). Two pass encoding provides the best quality per file size and is a good choice assuming the cpu is fast enough to handle any bitrate we throw at it (which is true for desktop but not quite true for internet tablets). So some scenes may get too high bitrate and choke your 770/N800 cpu. By the way, there are some interesting mencoder options (vrc_maxrate and vrc_minrate) which may be used to specify lower and upper bitrate boundaries according to their description. Probably trying these options with two pass encoding may help to avoid framedrops.

But if you don't care about file sizes and want the best quality possible, I suggest to use a high constant bitrate and single pass encoding.