I've got much the same with stock valves and it's fine. I'd resist the temptation to have bigger ones. You're not going to rev a van.
You would find I think that the peak torque would move higher up, and the maximum power would reduce with a lower CR on the same displacement. In other words spend money and make it meh. Next you would have to change the crank etc for more displacement All the time the cooling is still for a 1600 so attempts to go faster for any time without extra cooling will just result in running hot.. Fit an external oil cooler.. I benefit from one even with a 1641 driving hard..
I am thinking about putting one on although my van doesn’t seem to get too hot even at motorway speeds for prolonged time on summer days it rarely goes over 100 I find those earz seem to help a bit
