The power loss for a gear drive is, as I recall, negligible. As far as the crank harmonics, as long as you're balanced well in the reciprocating assembly, there won't be harmonics worth transferring.
I have found that gear drives reward careful engine builders. I'd not recommend them for just anyone - but if an engine builder knows what he's about, they're not a problem.
Crankshaft harmonics are part of the reason that you can get belt drives (like Jesel) for Small Block Chevvy - but I'd still see that as a refuge of an incautious builder. If you want to eliminate harmonics, eliminate them at their source - the reciprocating assembly. Although, I've never really liked belt drives - from a longevity point of view...
I've known quality double roller sets to last a good half-million miles, and "silent chains" (the typical "laminated link" chain we all have) can last anywhere from 200kmiles to 500kmiles and upwards. In some cases, I've seen "silent chain" systems last upwards of 500kmiles - which I count as only "slightly fluky" - it's possible, but unlikely.
Did you ever say why you were considering replacing your timing set? It may not be necessary - in fact, it's unlikely that you do need to do so, unless you are having a number of other problems as well...
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