Hmm, actually I think FTP may be triggering the CPU high also partially becos its ALG traffic:
NS208-> get nat registry vector | i ftp
1 00621f5c FTP
29 0060e970 TFTP
NS208->
I think you can try to have 2 specific policies :
NS208-> set pol top from trust to untrust any any FTP permit
policy id = 4
NS208-> set pol id 4 application ignore
NS208-> set pol from trust to untrust any any any permit
Pol 4 will ignore the ALG processing and the nxt policy will permit the dynamic ports.
Take note that you have to have the permit any policy facing the side where the server is starting up the data connection(if you are using active FTP). If its passive then you need to have the policy from where the CLIENT starts up the data connect.