hey we have the same bike
anyway, dynoman stuff can be trusted, he gets it from reputable sources. a lot of their products are geared towards perfomance. if you want OEM parts, look at david silver spares (they have separate US and UK/EU sites, google them based on your location) or cmsnl.com. these have almost everything you may need. you can find things often a bit cheaper online if you spend time searching. best to look up the honda part number in the partslist, and stick in google.
one good thing about these bikes is that you can actually still find OEM parts in abundance! hope the above pointers help you find them.
oversize valves flow more volume. with a stock engine they make no sense. if you modify your engine for performance then you can consider them but there's more to it so if you are thinking along those lines... better open a new thread stating your goals and asking which mods people recommend.
viton seals are dependable. and they resist today's pump gas with ethanol so get them while you can
racing springs and ti retainers, sames as the valves, if your engine is stock there's no need to spend the money. get a set of OEM ones.
as you're talking about replacing your valves: how are the seats? did you consider lapping or re-cutting?