bzr diff too slow (cpu intensive) on large projects

In general the experience with huge projects is sub-optimal in comparison to other VCS. A particular example: I have a --no-trees local repo of lp:gcc and a single --lightweight checkout in a local directory where I work switching in-between all my branches. Both dirs are on local disk (I've had *awful* experience when on NFS but that's not the case).

The following command takes about 2 minutes on a recent quad-core CPU and is mostly CPU-bound. Here is the full report from the 'time' utility:

$ /usr/bin/time -v bzr diff -rbranch:../notrees-repo/trunk > /dev/null
Command exited with non-zero status 1
        Command being timed: "bzr diff -rbranch:../notrees-repo/trunk"
        User time (seconds): 91.23
        System time (seconds): 12.81
        Percent of CPU this job got: 84%
        Elapsed (wall clock) time (h:mm:ss or m:ss): 2:03.53
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Maximum resident set size (kbytes): 369488
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 30
        Minor (reclaiming a frame) page faults: 4319360
        Voluntary context switches: 8765
        Involuntary context switches: 498
        Swaps: 0
        File system inputs: 277288
        File system outputs: 880
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0
        Page size (bytes): 4096
        Exit status: 1

Memory usage is also a (smaller) problem, as you can see max RSS is about 370MB, which seems too much for diffing files. I am trying hard to use bzr for gcc development but I can't say I have seen a lot of activity on all the performance or memory related bug reports.