I dont have a T 18 yet. I am trying to figure the order of priority for my next few Festool purchases.

Will I see a substantial benefit using a T 18 rather than a Dewalt 18v impact driver? The current project is framing. So I'd be driving 3" screws into 2 X material all day long. Also sub-foor decking. Thanks

Impact driver for what you're doing. 

You won't see any benefit doing this with a T18, in fact, you'll see the opposite. If you're driving such screws al day long you want an impact driver.

The Ti15 impact s great - I have one.

I'm hanging out for the latest version of the Protool PDC18-4 the thing is awesome.

I don't think you guys have got the Ti15 yet ... can't imagine Festool keeping the Protool drills away from the NA market much longer ... at least not the cordless ones. 

I'm a contactor and I agree with the Dewalt suggestion.  I'll even take it to the next level.  Dewalt's 18volts are becoming a dinosaur.  They're pushing their 20 volt line.  If you don't have a Dewalt, make sure you visit their website and find the drills that have at least 420 (preferably 450) or more UWO.  Believe me... You'll appreciate the extra unit watt outs if you're driving 4"ers all day.  A 700 series 18 volt at Lowes has significanty less torque than the 900 series.  Hence, the price difference.  Gosh, I hope Protool makes its way here soon.  When they do... eBay will be flooded with my Dewalt's.

They outlast drills when repeatedly driving large fasteners. I know this because my panasonic has driven hundreds of 8" screws where the t18 completely died after about 100, completly cooked it

Uh, are we talking about dedicated impact drivers or the drill/hammer units?  That's the beauty of the higher end drill/hammer  Dewalts.  You can quickly adjust for drilling then flip to hammer mode for smaller lags and subfloor decking.  If you're talking about lagging 10"x5/8" then that's certainly a dedicated impact tool.  Although, I have the Dewalt 36 volt drill/hammer model 901. Man, I challenge you to find a more powerful domestic cordless unit.  Trade offs are price and weight but does that thing scream power.

I'm guessing he really means tapped the battery ... if it killed a T18 I think he would have made a bit of noise about it elsewhere by now.

Dean ??

That battery seems to last forever on the Ti15 ... using it today - didn't charge it, didn't charge it last time either 

                     As many posters above mentioned, the difference is night / day, when it comes to driving large or hard-to-drive fasteners.  The difference, as mentioned, is the amount of force you must apply to the fastener head to prevent it from stripping.... with driver, you must apply forces equal to the resistance of the fastener.   With an Impact, hardly any pressure is required as the Impactors takes hundreds of small whacks at the head.  Then there is the wrist issue, specially if you drive fasteners all day.   A driver tries to apply opposite force to your wrist, so you must grip tight and your wrist exerts anti torque resistance continously.... an impact driver takes hundreds of tiny hits, not torquing your wrist.   IMO, the Impact Driver is one of the best innovations the fastener field has experienced in a long time...

                        Now, OTOH, if the force required to insert a fastener is minimal, such as small 1" screws into well drilled holes, this differences becomes irrelevant.... and the ratchet capability of the driver now offers more benefit to prevent stripping of the wood threads as the fastener head becomes seated.   This is what makes the CXS so spectacular, its low speed torque, makes it the ultimate small fastener screw driver.   


                                I have the 18V DeWalt drives, which are amazing...they have more than ample power for 5/16" lags, up to 5" long.... that is largest fasteners I drive, and this little yellow gem eats them as an appetizer..    Can't fathom more power.... of course, larger fasteners or higher torque fasteners might benefit from added power.   


Does the 24v provide more torque, or just longer amp hours?     

In my case, I never wear out the batteries, and if I do, the one on-deck is always waiting, so I appreciate the lighter weight of smaller batteries.   If you drive fasteners fasteners continuously,  some obvious benefits to larger batteries....

I BELIEVE the general consensus is that Torx and Robertson (square) heads are much better than Phillips. I'm partial to Roberston (Canadian ,eh?   ) Posidrive is another option. There are MANY different types of screws that are superior but some are very specialized, hard to find and even getting bits is difficult. This is an interesting article:

when is a Phillips not a Phillips

sorry been on holiday. Yep it cooked the drill. it did the double beep but then never started again. Came back with new electronics motors etc. Not sure if it was my t15 or t18 as it got replaced at some point but i have broken both models. I do work my drills hard but spoke to festool to see if what i was doing was with its range of acceptable activities and they said yeah its fine.