So far, the biggest cause for slowdown in CritiqueBrainz are requests to MusicBrainz web service. It's not that MusicBrainz WS is slow, it's just that some pages on CritiqueBrainz require a lot of MusicBrainz data, which might take a very long time to retrieve. This can be caused by the complexity of a request, or by a number of them (when showing multiple items, since there's no way to do batch-requests).
New infrastructure allows us to easily read data directly from the MusicBrainz database. Doing this in CritiqueBrainz will probably be a significant speedup.