Ok, so finally tried out the EPSi using the supplied ir's and first impressions are that there is a subtle yet significant difference.

I tried it with both clean and dirty rigs and stuck to two factory presets (10 Cent Sack & Snappy Tweed).

The best way I can describe it is, that there is a more 3 dimensional sound (i.e better soundstage). It's the kind of difference you would hear between a very good set of HiFi speakers vs a really great pair!

Only limitation I have found so far is that it would nice to have midi control over it so you could change the ir to match the rig on the 11 rack instead of having to dial it in on the EPSi.

Overall I am pleased with the purchase, next step is to try some of 3rd party ir's...when I find time again!