x264 normal I posted is identical to the current AVCHDcoder output except for for enabling psy-trellis with --psy-rd 1.0:
0.25 which is a minimal slowdown (>1% in my tests) while keeping details that are otherwise lost. Also --sar 1:1 is default so it's not really needed in x264 command line.
If --preset fast isn't as fast as you'd like maybe test out --preset veryfast it's about 50% faster but lesser quality. Also --psy-rd 1.0:0.25 can be used with --preset fast since --trellis 1, it won't have any effect with --trellis 0 which is what veryfast uses. Another option to speed up 'fast' is using --preset fast --trellis 0 the speedup won't be as much as veryfast would be but also the quality weren't be affected as much.
Your guess is as good as mine on --vbv-maxrate --vbv-bufsize and AVCHD standards. I've never seen much documentation on either. I haven't noticed and issues on a panasonic BD30 or PS3 with 24000/24000 and RipBot264 has been using it for awhile with no reports that I could see. But that also doesn't include video muxed with HD audio. My suggestion is if you can reproduce the stutter it try 18000/18000. If it still skips try lowering the bufsize to something like 9000 or so. If it still happens try using (18000 - <audio bitrate>) for maxrate/bufsize.
Oh and with slow and normal commands I posted it should be --direct auto instead of --direct-auto. I edited it.