It's more idiomatic to say "the pinnacle of development" than "the summit of development". The problem is that the name "Pinnacle Development Group" has already been taken more than once. "Acme Development Group", "Peak Development Group" and "Summit Development Group" are also taken. Maybe you could get away with "Optimum Development Group". There's a company in Florida by that name but Google only gives a handful of results. Ditto with "Optimum Developments Group".

Either Summit or Pinnacle would suffice, both are homonyms for mountain top.

I think I will pass :)