It sounds like you will need to make a lot for changes from roast to roast as well as having more independently variable controls to be able to change parameters while still having a rock solid platform. In this circumstances, I do not think that a traditional type non adjustable spring lever like the izzo Alex leva or profitec Pro 800 will suit what you are looking for unless you like taping thermocouple leads to your machine and flushing the lever many times to raise its grouphead temperature or using such home made work arounds as wrapping cold towels or locking ins fresh and cold portafilter or soaking in cold water the portafilter to lower the temperature.

If money is no object and you want a truly ultimate lever machine that there is no other lever machine that is even possible to upgrade to, then the two group kees van der westen slim Jim idrocompresso or a single groupLM LEVA X may be where you should go to check them out and see if they are what you want.

For a spring lever machine that will do almost everything those levers will do but at a small fraction of their monumental prices and that will come in smaller than their massive footprint, then it seems to me that there are only three real candidates - the nurri L-type leva and either the acs vesuvius evo or the acs vostok single group. Which one you prefer will boil down mostly to aesthetic preferences and whether you prefer a rotary or gear pump and whether you prefer controlling the machine more through a more tactile and minimalist interface or through touchscreen.

I have the nurri leva and it is easily the best espresso machine I have ever used or owned from the versatility, performance and the looks perspectives, and this is speaking as a former owner of the traditional non-adjustable izzo pompei spring lever whicj was very good.

The Londoninium r24 doesn't allow you to adjust the temperature of the grouphead independently and directly so it belongs in a different category than these machines.