The titanium valve is for the High end user(meaning big bucks/Racing)Not very cost effective for a daily driver/Weekend racer. You can do like
$um Fun said Change the guides out to run a 7mm stem.On the inatke use a nail head Or you can run a tappered stemed valve.Either will help the flow.(The nail head is a heavier valve) On a street Head you have to check the clearance on the valve guide with a tuliped valve.The Valve guide Boss needs to be shortened.UNLESS you special Order the Valve and tell them Just where you want That tulip to start at.With a Turbo you use a stainless Valve Or a inconel Valve Which can with Stand the Most exstream Heat(1800 degrees)(made for Exhaust Only).
Now as for the hitting water issue, It is More so of a issue IF(??) you deside that you want hardened seats installed in the head then it is the valve size. Even with a stock size Valve If a Deep seat is used You Run a much HIGHER RISK !!!!
of hitting the water jacket.Over Useing a Short seat. And This Becomes more of a issue with the Bigger Valves.This is all Due to the core shift in the heads.
So you have to watch what machine shop you pick.If they have never Played with or have any clue about our L6 heads It could cost you in the long run.Because they could hit water when installing a hardened seat If they go to deep.
BUT that is a risk any shop can find/run into Depending on the CORE shift of that Head,When trying to install a hardened seat.
You can also install a set of Bolt-in lumps which
will help improve the air flow. Even with a stock
size intake valve.
God doesn't like ugly.
