whirlpool is just longer... You are a expert?
This was tested with 1024000 bytes (1000 KB) of random data
Results: (in microseconds)
whirlpool - 64682.96
md5 - 6890.058
sha1 - 8886.098
sha384 - 45102.119
sha512 - 45655.965
Source
php.netIt maybe longer but the fact of it using
Whirlpool: 3bff3f475277fd87357cd4d2fc97a134af5efe570910d21f
1185e391f78f7d4b7c33a0a289efe1632b2026d77074ff50
7691c24c9782c5cce654dd01ea446a15
MD5: e6bdf8faab4a42ab37e3e833641dfe90
SHA1: abe7076758e0937c13743d26f9323897b57cb4dc
SHA384: bb7b69c28c09d42212ec83ed40e2b3454233c72fd2c268c2
fbcce477312d65e4fb36382235bc3febadde73660ffbeb4a
SHA512: a5179ffb67450eb83f8cdd915ee8c3037bb4d87f7e677311
819d5fb3dafaf54ac4c55405c7997adad8df3d6615964dda
5aa67acf27ea4c62e1d40f049b531d81
Different hashes ain't "just longer strings", Whirlpool is one hash i've always wanted to explore and considering you say it will use more space then i wouldn't want to be on your hosting.
Maybe do a little research into encryptions/hashes and you'll work out they ain't "just longer strings".