if CPU time is the bottleneck ...

Triple DES aka 3DES is only the default for SSH protocol version 1. You should not still be
using version 1 unless you are somehow unable to upgrade (e.g. device is physically
inaccessible, and has no firmware upgrade capability). Version 2 fixes important design
mistakes which have potential security implications.

When using version 2 clients and servers do negotiate, and the default between two OpenSSH
implementations is AES. AES was chosen because it is standard, and it became standard because
it is fast yet strong - Rijndael was the product of an experienced cryptographic team whose
earlier ciphers had proved well designed. During the main AES process all the participating
teams did extensive cryptanalysis of their own and each others ciphers, no serious problems
were identified in any cipher. Rijndael was eventually chosen over Twofish (a blowfish
successor) and three other contenders to become AES.

Blowfish is probably (I haven't tested) faster than AES, at least on some hardware, but not
enough to justify the small yet not at all imaginary uncertainty concerning its strength. Why
risk using something other than AES if you're going to bother using all those CPU cycles to
encrypt something at all ?