About the only time I've heard the .270 Win mentioned outside of say, a very rural sheriff's posse, is one of the local police SWAT training seminars that used to be held south of here a ways. A good friend of mine attended it regularly as an instructor... he mentioned some prison guards from one facility had some rifles in .270, and that they were surprisingly effective - kind of rough on the steel targets for whatever reason.
Otherwise... most of the other arguments for the .308 ring true. You can buy pretty good factory match ammo from either Federal or Black Hills. If you may even remotely consider using this as a 'duty' rifle, I'd make double-damn sure whoever builds you a rifle ensures it will cycle reliably with FGMM ammo (which is a little on the 'fat' side). Minimum spec chambers are not what you need here - both from the standpoint of you ain't shooting BR with the thing, and from the aspect of you want absolutely no ammo issues to come up... ever. Good news is, the .308 shoots disgustingly well with most chambers - no need to spec a custom chamber (sorry Al) with particular features. Pick a good gunsmith with experience in this particular area, and trust him.
IBA is a good choice; other good 'smiths include GA Precision (George Gardner), and R&D Precision (Randy Cain in Glendora CA). Actually there are a pretty fair number of them; GAP does a lot of 'volume' business and seems to have a lot of very happy customers, Randy did my rifle for me and it flat out shoots. I specifically had him go back and headspace the chamber to fit my GO/No-GO gauges (tighter than the ones that Kiff sends out apparently) that I use to set up my Savages but then my guns pretty much *never* see factory ammo - I'm not a cop wanting to do the sniper thing, I just 'game' with it in practical/tactical matches so I bear the full responsibility for it working (or not) myself - no ambulance chasing lawyers to worry about (with due apologies to any lawyers reading this).
Actually, for your 'first' rifle of this sort, a factory 'tactical' package like some folks have mentioned might be a better option... a 700PSS or a Savage 10FP w/ the HS or McMillan stock, a good mid range scope like a Leupold 3.5-10x w/ the Mk IV turrets and spend some quality time with the gun learning to shoot from various positions, working the bolt efficiently, etc. When you wear out the first barrel
or otherwise think you're ready to move on... you'll have a better idea of what *you* want in a custom stick.
YMMV,
Monte