The good ole 50-08 or 52-08 (the latter for traditional folks).   Depends on loft of your PW.  50-08 can be bent to 51-09 and 52-08 can be bent to 51-07.   The standard set gap wedge is 51-09.

You CAN hit a 50-10 or 52-12 off hardpan with some practice (play it back in the stance).   Either one of these bent to 51 = 51-11.

Also have to think of other uses of the gap wedge, such as hitting long bunker shots.   That being the case, 50-10 maybe.

Should visit a fitter to see which works best for your style (slider = lower bounce; digger = higher bounce; shotmakers can use the digger bounce because they play slider shots in soft conditions).

I use a 52-08 SM4.

as little bounce as possible. bump and run whenever possible.

I play the same conditions. Have a 52-08 Spin Milled and LOVE it.

IF you're ONLY going to be using a GW specifically for tight lies and hardpan, then, depending on the loft of your PW, and if you're pretty creative with your wedges, then you'd want a wedge with the lowest bounce possible. However, it also depends on your swing style. If a wedge is made stronger, then it loses roughly 1* of bounce, if you make it weaker, then it will add roughly 1* of bounce. 

As others have mentioned, it's just as important to be fit for your wedges as it is for your driver and other clubs. Click on this link: http://www.titleist.com/find-a-golf-shop/     to find the closest authorized Titleist rep to have them fit you precisely for your gap wedge. Try to find a Regional or Advanced, Fitting Center. They'll have more options and usually do their fittings outdoors. 

Let us know if you have any more questions. If you go get fitted for your wedge, let us know how things went and what you ended up getting. Best of luck to you!