Delhezi and senegal are about the same size but I blieve delhezi may grow an inch or two longer than a senegal. A 40 should be fine but 75 would probably be ideal.
always go bigger if you can go bigger.... i had 10 small endlicher 8" and 3 ornate 6" in a 90 gallon...tank was only a grow out but i had no problems...
I've got a 75 and have 3 Sens and 1 Delhz at the moment with some Mollies in it and they are loving the room! Could probably add 2 more(upper jaw) polys too.
I saw new tanks size,s at my local fish store 48x18x17-63gal, 48x18x13-48gal,48x12x12-33gal, 63 gal and the 48 gal are good tanks for Senegalus and Delhezi and Palmas ,s the 63gal was136.00, the 48gal was94.00 and the 62.00 the were made by all glass or AQUON or what ever its called