Now I have my codex, I rather like the idea of the 30-termy army as suggested by Boss Salvage above, especially in a 1850 point list where you have points left over for useful stuff like:
- combi-meltas (or combi-
plas) for the 8 non-reaper termies per squad - not too expensive and very nasty
- give the sorcerer wings, to get him into a better position for the termies to deep strike next to next turn
- change the troops to 10-member Cult squads (which ever cult suits your style, Thousans Sons looks tempting) and maybe give them a rhino and/or a icon-bearing champ - again to help the termy deepstriking
- maybe upgrade the termies to a cult, costs no more for a 10-man squad than a 3-man squad
That's a 51- model army, 30 of them termies, very hard. Not a huge amount of shooting once the combi-weapons have fired, unfortunately. Ideally there won't be many targets alive by then of course

but that's easier said than done...
PS the new plastic chaos termies are great!