What is the best graphic card for transcoding ffmpeg?

Hi , I use ffmeg with nvidia for vod platform . such as transcoding , watermark … .

I have a linux system with quadro p2200 and ffmpeg , all the things is works fine but I want to reduce the time of transcoding .

for example a 1080P video (55 minutes) (900 MB) gets about 30 minutes to convert to 144 , 240 , 480 , 720 , and 1080 quality in this gpu ,

I have a question about what is the best gpu for this purpose ?
and what are the important factors for choosing gpu for transcoding !

thank you for your help . .