Driving from Munich to Maria Alm in Austria

Dear all

This really is a question that I should be answering rather than asking considering how many times I've done it but it's always been the same way. I'm looking for alternative routes

The usual route is round the outskirts of Munich, onto the A8 to Siegsdorf then on from there via Lofer

I do,however, remember one such journey turned into about an 8 hour drive because of the mass of traffic. It was during Bavarian half term and this year the holidays clash again so I'm looking at alternatives to consider

Google maps does give alternative via Pinzgauer Str/B311 but I have no idea if they are our A road equivalent or country roads
Does anyone have any experience of that or any other routes which may avoid huge tailbacks?
The A8 tends to clear after the Innsbruck turn off from memory so an alternative route to there could also work I guess

Also, if I were to keep to the usual A8 route to Siegsdorf, am I right in thinking I don't need a Vignette to get to Maria Alm?

Any help much appreciated

Thanks