Manifold won't be that quick... At least not 8.12 x64 using quad core, 8gb ram and gtx 260. And that's because it does not yet use cuda for interpolation
A very good choice in manifold is flat triangulation and doeas nearly as well as DEST. Nearly as there are differences mainly at peaks and valleeys. It is much quicker though.
A very good test is to generate quite dense contour lines from dem (I used srtm 3 and contours generated at 10m interval).
Flat triangulation of dem of 2500 x 2500 at 3'' took under a minute. I had to cancel DEST after 20 minutes. It would finish interpolation eventualy but I had no patience to wait - after many tests in the past I found out that DEST seems to be best when the data are simplified and normalised prior to interpolation. DEST will then perform quickly and there won't be a big difference between dem flat triangulated from source counturs and dem interpolated using DEST from simplified data.
If you're interested, here: http://forest.miiz.w...mp/testdest.rar
is a test file. It containnes 3 drawings:
1st has the contours generated from srtm3 - flat interpolation instant, dest takes long time, both with pixel size 3''
2nd has the same contour lines but the topology was normalised (it took roughly 30 mins to do so) - once again flat interpolation is instant and dest takes long time, both with pixel size 3''
3rd has the normalised contour lines simplified at 1'' - here dest is instant, pixel size 3''
When compared, results of a flat interpolation using the source lines are very similar to dest interpolated dem from simplified lines. Dest handles peaks and valeys better so that's a good place to compare the output.