Is Raspberry adequate?

Hello there, new XBMC user and Pi owner here. I've played with the Pi over the weekend and came out with a few questions I hope the more knowledgeable and experienced people here might answer.

1. While 1080p@30fps and 720p@60fps H264 play fine on their own, advanced features of ASS subtitles make the Pi choke even on 720p@24fps (think 1 - anime karaoke = text with moderate effects, in mkv-supplied font undergoing some color and maybe shape/size transforms, and 2 - translated signs = rotated, perspective-distorted text with lots of font effects, polygons to cover the original text, all panning across the frame as the scene moves, etc.). Is this performance hit to be expected on any Linux implementation of XBMC, inherent to the subtitle renderer used, or is it just a bug that might be fixed soon? If it can't be helped, can it be worked around, eg. by disabling text styling and effects, leaving only basics like size, color, 2D rotate and positioning?
2. External mkv chapters don't work - the "next chapter" button just goes to the beginning of the current one, and playback skips over them - again, is this a bug, or are xchapters just unsupported?
   

Thanks in advance for any helpful replies .