If server based proposition would have been costlier or there would have been problems in scaling beyond 200 seats in a server based solution then Market Leader(74% installations in India) DAVOX would not have opted for Server based solution provided by a much smaller player like CELLIT Technologies and would not have merged to form Concerto softwares. for more info you can go to web site of Davox.
I can assure you a 1000 seater with blended agents and working quite satisfactorily using Server based technology.To prove it further I can refer you name of our client currently using server based technology for 350 seats in Delhi.
DO NOT WORRY GO WITH THE SERVER BASED TECHNOLOGY FOR MULTIPLE LEVEL REDUNDANCY AND SCALABILITY. WHICH IS CHEAPER YET FLEXIBLE WITH OPEN ARCHITECTURE.