Inconel isn't really any stronger than stainless. It's just more heat resistant. Now of course that translates into more durability in a higher performance engine, but in something like a 350-400 horse engine they'd probably be even.
Having said all that, if you aren't in some extreme application like high-lift cams or blowers over 5 psi and you're not running super-lean, you should be able to get 350-400 hours out of a set. Valves are pretty cheap- relative to a broken motor or a lost season. I wouldn't do a top end and reuse them.