That is one approach you can take. However, there are hazards.
At only $16 I think I'll get a SS valve just for lapping and then check the fit of the Ti valve. I have a 20X optical micrometer that I use to check the contact width and placement and also surface condition.
First, you need two valves at minimum, so now we are at $32 for your throwaway lappers. Second, when lapping, as the seat begins to take on the perfect, ground shape of the valve face, the valve face begins to take on the worn, irregular shape of the seat. So, even though the SS valve is probably somewhat harder that the iron seats used in YZF's, when you lap your second valve, the valve you lap with is no longer the brand new, perfectly ground piece it was to begin with. Then, on the intakes, there are three.
Valve float is a non-issue once the right springs are in place, and no one has ever verified that the CRF, for example, ever suffered from it. Neither do the current R1/R6 models, which are also 4 valve, and operate reliably at engine speeds that makes the hair on the back of my neck bristle to even think about.
Exhaust valves can be and in fact are smaller than intake valves since the gases are forced out. The intakes need to be as large as possible since the gases are simply drawn in by vacuum. But if they are too large, valve float becomes a problem at high RPM's with resulting valve damage.
The real reason exhaust valves are smaller is because the the exhaust gases are less bulky than the intake mixture because the fuel has been burned out of them.
The Genesis 5 valve head design was originally introduced in large displacement road bike engines, and the intake configuration was designed to improve mid-range power and fuel efficiency. It has a distinct tendency to stratify the intake charge somewhat in the manner of the Honda CVCC 3 valve engines, concentrating the bulk of the fuel at the center of the combustion chamber and surrounding it with a much less fuel-dense charge of air. It was never intended as a means of producing maximum top end power.
Using three intake valves allows a larger intake cross sectional area using smaller valves. The smaller valves reduces or eliminates float at higher RPM's thereby increasing reliability. Or perhaps longevity would be a better word.
Continuing from the above point, charge stratification is a handicap from the standpoint of maximum power production, and short of placing 3 discrete injector nozzles in the ports, is unavoidable in the 3 valve intake. A much larger problem exists in getting the port to flow well. The additional port divider and valve stem become obstructive beyond any gains made by have larger valve area.
I do not understand how more top end power is achieved with two rather than three intake valves.
In fact, ideally one would choose to have one port each for the intake and exhaust, but the ideal combustion dome in the head is a relatively shallow concave shape. With that, there is a limit to how large a pair of valves can be made and still fit into the available space. The engine will normally be potentially capable of using a larger intake and exhaust area than can be had with two valves. By going to two of each, the port area can be greatly expanded. The additional valve stem, valve head, and port pocket on both sides, are an added liability, but their negative effect is out weighed by the added benefit of increased total area. Likewise, the port divider, an obstruction on the intake side, does not hurt more than the increase in area helps.
But when you compare 3 intake valves to 2 within the confines of the same combustion chamber, there is no significant gain in port area that can be made versus using two valves, and the additional flow restrictions hamper maximum performance.
Ron Hamp, one of the nation's premier engine builders in flat track competition, long ago produced CRF450's well beyond the 60 HP mark, but it took him until last year to do the same with a YZ450. The head is the limiting factor.
I love it when people do that. I did not say "there is nothing harder", I said almost. Most abrasives used in lapping pastes are hard enough to damage the hard coating, hard as it is (off the top of the Rockwell scale), and the problem with that is that the coating is less than .001" thick. ANY damage to it would be intolerable, and reduce the life expectancy of the valve.
And if there is nothing harder than the coating on a titanium valve face, I do not understand why it would hurt to lap with the titanium valve. That said, I will certainly defer to Eric Gorr's advice on not lapping them.