Living in zone 6B in Maryland, overall, which is the better fig for my area, Italian 258 or Col De Dame Grise.

For flavor, ripening, cold tolerance etc.

Thank you.

Given your zone, the more reliable variant for bountiful figs would be RdB. Both I258 
or CDDG needs a longer season. 

Ditto to what Paully said. Get a GH if you want to taste those figs in your climate.

Italian 258, to answer your question as asked. Of course you should have an Etna fig for reliability, RdB will not perform well for you without the same level protection that I258 or CdDG requires.

If you have a totally full sun location,(10 hours or more), both will ripe,and both are top tasting.
Protecting from Winter,it is possible,if you want to.
Not a full sun location:they will not ripe,properly every year.!

I will recommend Michurinsk-10 (syn. Florea I think) Very hardy, and early figs giving tree. This var. is from Bulgaria. But I can't help with Italian 258 or Col De Dame Grise cuz I don't have them. 

Greetings from Poland 

Out of the Col De Dame figs Grise would be the one to try as it ripens earlier. I agree with other comments that you should try ones known to work in your area so you will always have figs, and then experiment with these other long ripening types. MBVS would be another to get. I have an unknown found in MD. It originated in Italy. It's called
Unk. Teramo. Seems like a very nice tree, but mine is first year, so no opinion as of now.  From Teramo in the Abruzzo region.

All my Mt.Etna figs ripen later than RdB. In my 6/7 zone, my Rdb's are never protected -- whether in the ground or in pots. My I258 & all CDD's variants need protection. Definitely late producers. Usually for main crop figs, the earliest to ripen for me consistently have been Florea followed by RdB -- about a week or 2 behind Florea by around mid Sept. However last season the winter was mild and so is 2016, hence most variants were about 3 to 4 weeks early. As I write I am surprise my 1st 2016 ripe fig came from Martin's Unknown. Most of my breba figs are at a stage where ripening can happen especially Ariane and Morena.

Get a greenhouse and you can get Fico D'inverno to ripen .

Paully any container trees I leave out here will be dead to the soil line, or totally dead, so we do have different zones. RdB tends to grow instead of fruit after hard pruning and has been more sensitive to cold than most varieties because of the vigorous habit. It has had 3 years to ripen the first fig of the year and maybe this will be the year, I used 150  gallons of leaves to protect it.

RDB in my zone 5 area is very productive and I haven't noticed any reluctance to set fruit after a hard pruning. I do normally pinch the tip out at 4 to 6 leaves on new growth.
My in ground RDB ,with protection ,has made it through the last 3 Winters here very well like the others I have in ground Florea and MBVS , so no real cold sensitivity that I've noticed here.
It certainly is vigorous , that's for certain.
For me , if I weed out a variety it is most likely being replaced by another RDB.

My Italian 258 is to young to have fruited yet for comparison to CDG , maybe this season it will fruit.

Kerry, my in-ground RdB here produces a reliable huge crop. Seemingly it is a variant that does not require a long
period to ripen main crop figs. This is excellent -- I get a good feed on them before I immerse myself in salmon fishing.
I have 5 RdB plants -- 2 in-ground and 3 in pots. No protection for my in ground trees. I have no issues prunning Florea
& RdB hard for main crop. 

Well guys, I hope you are right, I have planted out over 2 dozen RdBs now. 2- 4th year, 10-3rd, 20- 2nd. Plus the containers. 

Why do you have so many of the same fig?

Production plantings are always large numbers of relatively few varieties. It is more efficient and also important to have a consistent product.

let us know how things workout -- RdB could be a good alternative to Mission on a commercial scale.