Hi Nick
No, I didn't try out any other subwoofers. To be honest I think it would have been really difficult to get a true impression of the nuances of different ones at the Hi Fi Shop - it's not like auditioning stereo speakers where the differences can be quite marked.
I knew I didn't need anything with awesome power as it was for Hi Fi purposes only and my room is not large. The Rel Quake was well reviewed and cost about £350.
The one "downside", I guess, is that, as someone who can be a bit anorakish about sound I'm never satisfied I've got the settings quite right!