Rega RP8 or Technics SL1200G

Ralph, sorry, I’m not getting it. Have you listened to an RP 8 in controlled circumstances, and if so, how did it fall short? That would seem to be of help to the OP.

From your post I can only assume that the Linn LP12 is not a well regarded vintage machine, as “...all the well-regarded vintage machines.......have powerful drive motors.” I tend to differ on that point finding the Linn to be a well regarded vintage machine with a different design brief.

Since it was designed as a specialist product, rather than for cueing in radio stations, a less powerful motor was used as it produces less vibration than a high torque motor. What vibration is left is mitigated by the belt rather than being directly transmitted to the platter by an idler or direct drive. The trade off is less secure speed accuracy and the benefit is a lower noise floor. Those are intentional design briefs. And though you may find the resulting sound to be inferior, it seems very hard to think that saying that the Linn is not well regarded can only be the result of turning a blind eye to the historical significance and longevity of the product.

For a second I thought that you might not consider it vintage due to the age. But the SP10 came out in ‘70 and the Linn in ‘72.

Happy holidays and all the best,
Marty

Two items to consider.  Is the RP8 die for an update?  The difference between the RP6 and P6 is substantial.  Also something to think about is your listening space and isolation.  The SL1200G won’t need the same level of care and placement as the Rega.  Two small points in an otherwise difficult decision.  My feeling is that the 1200G is superior technology over the Rega.  

Here is Fremer's review of the 1200G. The 1200G is also an Absolute Sound Product of the Year in the January 2018 issue.

Pretty much every review I've read of Rega TTs that measures rotation speed indicates that they run fast, whether it's an RP3, RP8, or something in between. Since the brand has been consistently (slightly) fast for years, I suspect it's intentional. If I were to guess why, perhaps to compensate for a low-torque motor combined with a stretchy belt.

A high-torque design with great speed consistency has notable playback advantages, particularly maintaining tempo and volume in the face of higher groove modulation--modulation that accompanies louder passages and/or a higher number of voices and instruments.

Thanks everyone for your comments, they have been very helpful. 
@johnnyb53 , I've read both of those reviews, also one in Stereophile.
One thing that no one has mentioned is the dreaded Rega hum. My P3-24 suffers from this malady through the TTPSU, I believe. It's not noticeable during playback, but it is there while idling. I'm leaning towards the Technics. I'll make a final decision after the first of the year. Thanks again.  

I have an SL1200GAE with Parasound JC3+ and Audio Technica ART9 cart. This is a spectacular combination and the last vinyl setup I will ever need. Far exceeding the VPI Scout 1.1 it replaced.