Would ultra-efficient carbon sequestrion produce immediate results in global temperatures?
The issue of the lag time between carbon addition to the atmosphere and maximum warming that results from it, is probably pretty divisive. I had previously heard estimates around 50 years, but the most recent work I could find (that was available for free) indicates that 10 years is about right, with Figure 1 of the linked paper being the best graphical evidence. This 10 year response is for a one-off injection of carbon, so we can't assume it would work the same for a one-off removal of carbon, but we can go with that number for now.



So, looking at Figure 1, if we started rapidly removing carbon from the atmopshere, the temperatures should reflect within a year or two, and if we removed ALL of the anthropogenic delta-CO$_2$, we could expect temperatures to go back to pre-industrial revolution plus or minus any natural changes since then in about 10 years.

A side note: supposing we could sequester as much carbon as we put into the atmosphere every year. That would be great! But how much energy would it take to sequester that carbon? And where would we get the energy to sequester the carbon. Sequestration seems like a great idea, but I don't think it would work, even if an excellent method of sequestration could be found, until the world's energy demands are met from non-fossil fuel sources.