[Had to edit this post, line-breaks may be off...]

OK I've read many of your previous discussions in this area and didn't want
to take you back over old ground!.
I will mention a few things as relates to my installation:

1) The store has two 'stats to combat boiler cycling (you can blame Dr Evil)

2) My pump is indeed a bit slow (10L/min max), so much so that something
will probably have to be done.

3) The water sent to the current boiler (from the bottom of the 1300mm
store) seems to be surprisingly cool(ish) in relation to the overall
temperature of the store, the space-heating take off is high up which
probably helps. This should help condenser efficiency though may not be the
whole story!.

As for the boiler... pendulum swinging towards a 'normal' modulating boiler
I think. Apart from anything else, Quantum Heatsave seems to be the only
known specialist option. BTW can you really still get non-condensers?.

Egremont.