<snip> I'm not at all comfortable with thumbs forward, which I've tried before, and it's a slower way for me to get a two-handed grip from holster to presentation. Is the thumbs forward grip really all that much better?
Its likely not that thumbs forward is inherently slower, but rather, that you've not yet developed sufficent muscle memory to allow yourself to go faster. Slow is smooth, smooth is fast. Pro shooter Todd Jarrett is so smooth and fast with thumbs forward, that you simply cannot make a case for slowness being a function of a thumbs forward grip.
I'm going to link below a couple of YouTube videos of Todd Jarrett for you to watch. They provide tips on developing the thumbs forward grip, and as you will see, Todd is absolutely blazing fast at presenting and shooting his pistol -- with thumbs forward.
Sometimes it is the smallest of details that make the biggest difference in complicated sporting activities. I had this happen to me with just one tip on skiing. In that case, I learned to focus on driving my knees forward (down the mountain); and suddenly everything else just came together as it never had previously.
Same thing for me with shooting pistols. I had grown up with the Weaver stance, but had tinkered on-and-off with the isosceles stance for years. I liked the way the isosceles created more of a turret base from which to shoot at mutiple targets, but with my grip, it just never seemed right. Shooting thumbs high always worked with my usual Weaver stance, but not so well with the isosceles. So rather than changing my thumbs high grip, I went back to what I knew worked.
Some time back I watched Todd Jarrett teaching the thumbs forward technique (there are tons of videos with him out there). The one little thing that was missing for me, was not rotating my support hand forward. Once I rotated my hand forward 45 degrees, my wrist moved in line with forearm and the light bulb came ON! Just a little break at the elbows and now my hands stayed tight and steady and the elbows worked like shock absorbers. Way faster and more consistent keeping the front sight on target and working the trigger. Wish I had learned this a little bit sooner...
Watch this first video of Todd teaching his shooting stance and grip:
Todd Jarrett on pistol shooting. - YouTube
The second video is very poorly edited and hard to follow, but if you watch past those short comings, you will see at the 4:15 time mark, the exact rotating of the wrist motion that make the thumbs forward grip work.
Todd Jarrett shooting tips - YouTube
HTH