MM - the biggest thing is their "growth curve". Calves have a growth curve, and if their nutrition level is not kept up, you flatten our their curve. Yes, when you put them BACK on good feed, their growth curve will start up again, but will never achieve the high growth curve it would have had - if that makes sense.
Taste is achieved the last 60-90 days of feed, but Farmhand is correct - started on grain at a young age & kept on grain thru finish - they will have MORE marbling. Also, if you put them on a "holding - slow growth" stage, they will grow FRAME, not muscle, and therefore would need to be heavier at finish than if you kept them at a steady growth.
So, you will save money from the weaning time to the 800# wt, but you will lose that gain by needing more grain to get to the "finish" weight. So, in my opinion, you will be losing the time (and $$) from WW to 800#.
This is the same thing the old large framed Simm steers ran into. People would put them on a background program after weaning, than put into the feedlot and they ended up with 1700# finished steers at around 2 yrs old. But if they had put the 800# weaned calf right on the feedlot, they would have finished around 1300#-1400# at 15-16 months old.