I do not see that weight would make one better than another, just easier to lift and get on the lathe. If you are only going to use the chuck infrequently, then you might consider a less expensive alternative and/or a 10" six jaw chuck. You will be limited with a 12" chuck as to the opening distance of the jaws, and may need to remove the gap, the through hole capacity is limited more by the D1-6 mount/spindle bore.
A 12" Bison/TMX 6J is going to run you over 3K with back plate. A 10" Bison/TMX 6J would be about 1K less, and going with something like the Shar's 10" 6J Set-tru would be 2K less. I recall a few other individuals that bought the new higher end Shar's 6J and they were very satisfied with it performance and accuracy. You can review the specs. below they have them in 10" and 12", they are semi-steel so the max RPM will be slightly lower, but if you are doing larger diameter work you would be nowhere near the maximum speed ratings. They are Set-Tru style so the TIR can be adjusted withing 0.0005", and more often the issue is clamping with 6J the diameter of the work piece will be out out of round more than that.
Somewhat in ascending cost, they will all hold stock pretty much the same. Bison 12.5" with back plate will be about $500 more than the TMX. Just would be a hard swallow spending so much on chuck, unless it was your primary chuck for the type of work you do. A 12.5" chuck on a 16" swing is a bit too big, and only advantage would be the chuck through holes is just over 3" vs. ~2.9" and you are still limited by the D1-6 back plate/spindle bore. I just picked the eBay sites, on Shar's often shipping is less through eBay, otherwise I would go directly to Small Tools or Ajax Ind.
Shar's 10" 6 Jaw SET-TRU Lathe Chuck .0005" with Fine Adjustment
Find many great new & used options and get the best deals for 10" 6 Jaw SET-TRU Lathe Chuck .0005" with Fine Adjustment + TIR Certificate R[ at the best online prices at eBay! Free shipping for many products!
www.ebay.com
10" Bison 6 Jaw "Set Tru" Lathe Chuck + Adapter Plate
Find many great new & used options and get the best deals for 10" Bison 6 Jaw "Set Tru" Lathe Chuck + Adapter Plate at the best online prices at eBay! Free shipping for many products!
www.ebay.com
12-1/2" GATOR Lathe Chuck 6 Jaw TRU ADJUSTABLE FORGED +ADAPTER 1-103-1200
Find many great new & used options and get the best deals for 12-1/2" GATOR Lathe Chuck 6 Jaw TRU ADJUSTABLE FORGED +ADAPTER 1-103-1200 at the best online prices at eBay! Free shipping for many products!
www.ebay.com
Toolmex 12" Set Tru 6 jaw Lathe Chuck Made In Poland
Made In Poland Part # 3-868-1200P.
www.ebay.com