The Droid Turbo specs LTE 1700Mhz & 2100Mhz, which is LTE band 4 which AT&T uses, but more commonly they have deployed band 17 (700b)
LTE in the US is completely jacked up. Spectrum is split past all reconciliation. SO dont count on the Turbo dealing with AT&T's LTE worth anything, if at all. (Specs dont list the exact channels the turbo can do on band 4, so it may not be able to get AT&Ts.)
As far as HSPA goes, HSPA+42 is not in the cards for the turbo, with a maximum speed of 16Mbit via WCDMA (GSM 3G) networks. So expect real world max on GSM 3G to be about 7 - 12 Mbit down, tops. Also only T-Mobile uses HSPA+42, so to get that you'd need to us ST TMobile sim. I got nothing good to say about TMo, and you know what mamma says. \