Plinius SA301 Or Bryston 4bsst2?

Well, it's not a bad amp at all, I have had a 4BSST for 8 years now, you definitely can do worse. But alas, it's middle of the road stuff when speaking about top class equipment, which is very expensive, but they (Bryston) used to have prices that were commensurate with middle of the road stuff. Now that they've gone up in price, they're not the good deal they used to be. However, I must admit, in comparison to certain more expensive brands, Bryston holds its ground pretty well, and I for one, prefer it more to McIntosh most of the time. McIntosh can be a little too warm and slow sounding for my taste. I guess I prefer the faster and leaner sound of the Bryston more.

What do you think is better/best around the 4BSST 5K level Dave ?

The Ayre V-5, of course. It's not quite as powerful as the 4, but the SQ is in another league. That said, I wouldn't pair it with a Thiel without an audition. Its a more detailed amp and paired with all those metal drivers Thiel uses may be a bit too much. But its so good, you may want to upgrade your speakers.

I heard the V-5 on Maggies 1.7 last year at a dealer, not saying it was the amp, but it was horribly shrill.
Do they take a long warm up?

It wasn't the amp so much as it was a poor combo. The V-5 didn't sound good on my 1.7's either. It won't hide the flaws of other components.

The warm up is quick. When you turn the V-5 off, it goes into a standby mode that keeps the amp partiality warmed up.