I've tracked and mixed on an SSL 4040G+ numerous times, and I've never touched a Harrison before, so I'll tell you what I like and don't like about an SSL-
-General stuff that I like (based off of a G series)-
1. Options-You can do the same thing about 50 ways on an SSL using the modes and other controls. You can also move the dynamics, EQ, and inserts around in the signal chain to suit your needs. The modes are very cool to work with. You can move your Large or Small Fader into whatever signal flow path that you want, and you can control the output of those faders to either the routing matrix or quad buss.
2. Dynamics and EQ-The SSL's come with a compressor/limitor, expander/gate, and EQ/Filters on each channel plus side chain control. The filters are a 12dB/octave high and low pass, and the EQ is a 3 band with variable gain and frequency controls. The HF and LF can be switched to a bell curve from a shelving. The EQ's sound great, but the compressors can be very harsh. The compressors are amazing for rock drums and bass, and you can get good sounds out of it on guitar. The other nice thing about the dynamics/EQ sections, is that they are totally bypassed if you do not activate them. Also, the inserts have to be activated, so your signal isn't sent to the patchbay and back if you don't want it to be.
3. Quad Compressor-Fuck yes.
4. Automation Computer- Very simple to use, and very effective. A G+ series console allows you to automate the VCA faders, master fader, and cuts (mutes). Even if you do most of your automation in software, the SSL has machine control (using SMPTE, you have to have a special box to distribute the timecode so the SSL and the DAW understand eachother) so you can use your DAW as a tape machine and control playback functions (play, stop, rewind, fastforward) from the console without having to turn over to the computer. The Total Recall feature is fairly sweet also, which saves a "snapshot" of the console so you don't have to write down each channel's settings (you still have to for the master section). You just recall your setup, and the computer tells you if you have it dialed in right.
-What I don't like-
1. The Preamps-Sure they are 100x better than anything I have at my house, but when you have a Great River and a few API's in the room, avoid the SSL pre's. They can be very harsh sounding, and can add a lot of the bad, unwanted analog sound if you hit them too hard.
2. Depending on what kind of faders you have (Motorized, or VCA) will change the way your mix sounds drastically. The SSL that I work on has VCA faders, which use an amp to attenuate or raise your signal instead of an analog fader. These can make your mix sound kind of thin on the top. If you are used to them, you learn how to get around it, but if I don't have to use any automation I'll mix on the small analog faders. Also, VCA faders do not move. When doing any automation, your only reference for where the fader actually is if you moved something is shown by the computer screen. If you have Ultimation (moving faders), then they will move (and they sound a hell of a lot better).