From left to right...
1/A stainless steel aftermarket valve.7mm spindle and recut to 33mm at the head.
2/The mentioned Peugeot valve.
Again cut to 33mm head on a 7mm spindle.
3/Stock 102.983 exhaust valve.
33mm head on a 8mm spindle.Sodium filled spindle to cope with the heat.
Point here is that the progress in metalurgy has given that we don´t "need" the sodium anymore-which in turn only makes the valves more expensive.
Further if you take a look at this poor quality picture;
...you can see that the stock valve is a 2 piece design that´s friction welded together.Again...something that we don´t want in a high reving performance motor.
Furthermore the stock valve is made out of a VERY soft material.
Reasons for that....is beyond me at this point.
The stainless aftermarket valve is tough as a diamond.