Your clan tartan is completely appropriate for formal events. If you have seen universal tartans at formal events it is most likely because they were rentals, that are normally available in only a few, mostly universal, tartans.

Now, you will get many opinions as to whether a SWK Standard is acceptable for formalwear, but if you plan to get a 8 yd wool kilt, I would get your clan tartan, unless you don't like your clan tartan.