That's kinda strange, that a valve that wears the guide?.. I mean, chrome is chrome...... mostly. Better chrome is thicker more even, and more porous, but generally chrome is chrome.
Try some higher quality guides, what are you using? have you tried PEP? Are you polishing the stems of these used valves?
You want the best cooling, run tight, but you want the longest service life....shoot for the middle.
Running extra tight will cause more wear, and those wear particles will embed in the guide and scratch up the stem, and that's why extra tight wears out faster, tho it does GUIDE better, The #1 job of a guide is to guide.
If the valve is too hot for what the guide material can handle, then additional clearance does not help very much, you just have to go for better materials, or a smaller stem and just let it be hot.
The old rule of ratio for guide length VS stem size, is guide length should be 7x stem size. What is that ratio on these heads?