LOT of interesting thoughts in this thread ... I'll throw in my OPINION. And I say opinion as "people" are a variable which has no guidebook. There is no manual / instruction sheet for that part of the swing
I have had the opportunity ( or misfortune depending on your point of view lol ) of working with pretty high speed guys. And the bulk of the guys I choose to work with one on one are ALL scratch or better - so they can deliver the head to the ball. But that also allows me to answer with respect to a "golf swing" - just a little faster. Apple to an apple though
So before I go ... A tiny statement - NOT trying to get the Hatfield's & McCoys rocking. There will be builders who don't agree with me - and high speed guys that don't agree ... whatever .. no problem. Just a post on a forum
OK - 1st off ... NOTHING !!!!!!!!!!!! has a more dynamic affect on spin than driver loft - PERIOD. Driver loft is KING with spin. Lets face it - driver heads have been maxed out for years - the modern generation is all about manipulation of CG & launch conditions .. and they are all damn good at it.
Torque - For high speed - and for guys with "swings" not mashers (you would think it would be the opposite but it isn't ) - but HIGHER torque for a pretty high speed swings is your friend. Those guys can use torque to gain a few extra microseconds to come thru the impact zone and be square and in control of face angle. MASHERS - in my experience / opinion - like lower torque as there delivery is much more erratic and they just need head control thru the zone - they hold on - usually super strong ... I could go on.
I am in total agreement with revkev - For me - the weaker the shaft the better for most people. Most guys get on monitors and go for it - and admire their speed. Truth is - go out a look at trees & out of bounds & water hazards etc ... That monitor swing is USELESS in the real world. I always tell guys - Monitor minus 5mph. Also OVER-stiff will usually results in a wide open fanning slice at the ball - and spinning like crazy. I get guys in the weakest combos they feel good with. I will tell you - and this isn't uncommon - in the high speed world. Some of the most visible / multiple world champion type guys - use MUCH !!!!!!!!! weaker shafts than you would think ... MUCH !!!! ... Trust me
Balance. Eeeehhh ... I'll say this. Heavier head (204+ with adapter) - you want a little counterbalancing to maintain good weight. PIng is REALLY good at it (for an OEM) - Cobra is a close second.
Weight - The most important for me ... MOST guys - if the driver is built correctly - will be better with a heavier driver than they think. I am a GIGANTIC !!!!!!! fan of very short / heavy driver setups. Look at the Tour - MOST of the time - over time ... The big guns all use slightly heavy / shorter combos - with head CG manipulated to max given the end head weight
Flex - There is no standard - and there is a LOT !!!!!!! of bad info being pumped into the world regarding shaft tech. The heavier the shaft - the weaker you can play it .. Super lite ( which I HATE ) .. need a little stiffness to get some control. The exception to that is probably the older / weaker golfer. But even they can play weaker / shorter combos with LOTS of loft and get good results.
I could keep going ... Maybe I'll spill my guts one day ... but when I build drivers - PLAY drivers ( cuz even I don't give a damn about long drivers ) - I do everything in my power to get the to use short / heavy SLIGHTLY weaker than you'd think BATS .. and it works EVERY TIME.
This guy ....
DESTROYED !!!!!!!!!!!!!!!! the world in 2000 with a 43.50 in steel shafted Titleist driver
and won his first major - with a 43.50 steel shafted COBRA.
and he's never driven the ball better since .. and YES I STILL LOVE !!!!!!!!!!!!!!!!! steel shafted drivers
Just my 2 cents