FWIW, since I had a bunch of notes on this stuff and figured it might be of interest to some others.

Ever wonder what difference all those different lash settings make when looking at solid-lifter (flat or roller) cams? Here's a list of different lash settings and how they effect the seat timing for any given cam. I'm listing the duration points at both SAE (.006" valve lift) and "actual seat" (at the point where the lash is reduced to zero) since I've seen both used.

Lash --- 1.5 Lobe Lift --- 1.6 Lobe Lift
--------- SAE (Seat) ------ SAE (Seat)
.016" --- .0147" (.0107") - .0137" (.0100")
.018" --- .0160" (.0120") - .0150" (.0112")
.020" --- .0173" (.0133") - .0162" (.0125")
.022" --- .0187" (.0147") - .0175" (.0138")
.024" --- .0200" (.0160") - .0187" (.0150")
.026" --- .0213" (.0173") - .0200" (.0163")
.026" --- .0227" (.0187") - .0212" (.0175")

Does this really make much difference? Well, if two cams both share the same advertised specs at .020" of 290* and one is designed to run at .016" lash and the other is designed for .026", the SAE duration for the tight-lash grind is likely to be 300-302* where as the looser-lash grind is going to come in around 288*. So, yeah, I'd say that 12-14* difference in seat timing is going to be pretty obvious if you compared both cams in the same engine.

How about a cam where the lash ramps have been designed to allow a fair bit of lash adjustment to allow for some tuning? Does changing the lash make much difference to what the engine sees? Here's two examples I picked up from some Cam Doctor data published years ago:

Example 1 is on an intake lobe where the lash was reduced from .018" to .014". How much extra duration resulted?
.006" - 4.6* (SAE)
.020" - 3.4*
.050" - 2.3*
.100" - 1.6*
.200" - 1.2*
.300" - 1.2*
.400" - 1.3*

Example 2 is on an exhaust lobe where the lash was increased from .022" to .028". How much less duration resulted?
.006" - 6.9* (SAE)
.020" - 5.1*
.050" - 3.4*
.100" - 2.5*
.200" - 1.9*
.300" - 1.9*
.400" - 2.2*

In both cases the biggest change in duration was right at the initial opening/closing points, but the amount of effective change tapered off significantly starting above .100" valve lift.

I also wanted to comment on what really happens when cam "designers" start mixing & matching lobe families with dramatically different designed lash specs. I had cam that spec'd out 295/305 @ .020", 265/270 @ .050", 180/178 @ .200" w/ the provided lash settings of .018" intake / .028" exhaust. Anyone want to guess what the actual duration split ended up being at those lash settings? I'll get straight to the point and say that all that additional exhaust duration got "lost" w/ the extra .010" in lash and the split ended up being negative (less exhaust duration than intake) from .020" valve lift on up.