They should be extremely similar. the 20-39 should get a bit lower...
22Hz vs 20Hz
But even the website says they are virtually identical.
If you need more flexibility options you will want to step up to the "plus" series which offer continuously variable phase, multiple subsonic freq filters and tuning plugs.
You can email SVS directly for a precise recommendation on your listening tastes. But as for the two in your subject line, should be VERY close.