That reasoning made sense on Solaris but may have a problem now, given
that you're moving to Linux, because /bin/ksh on Linux is *also* junk.
This stuff is very very tangled and confusing ... briefly, /bin/ksh on
Linux tends to be a link to "pdksh" which is a buggy ksh clone, now
abandoned. The "real" ksh (ksh93) is actually open source too but most
Linux distros won't bundle it due to philosophical issues with its
license (boo). So unless you go out of your way to find and install
the actual ksh package manually you will have a broken ksh on Linux
and a broken /bin/sh on Solaris. Fortunately Solaris has been bundling
bash for quite a long time, so perhaps the most robust and portable
arrangement for you would be to settle on SHELL=/bin/bash.