Landlords pushing the rent envelope.

Up until recent years, to say that a deal was exorbitantly priced in Midtown, rents of $100 per s/f would suffice.

According to data from the commercial real estate services firm Cushman & Wakefield, 30 buildings received rates at or above that last year, a number that far exceeds the shortlist of high-end buildings that used to be the only addresses where triple figure deals were done.

As the unprecedented strength of the Manhattan office market continues to make formerly top dollar rents look more like the norm and expands the roster of buildings that can command them, landlords of trophy buildings have begun to probe just how high their rates can climb.

No longer pinned to the low $100s per s/f, the increases are pushing office rents for top buildings in the city into uncharted territory. But while the repricing may be a windfall for landlords, experts say that it could also prompt tenants to reexamine which buildings are truly worth top dollar.

At 745 Fifth Avenue, for instance, the building's landlord, Paramount Group, plans to raise asking rents to $160 per s/f for a pair of floors that are scheduled to soon become available near the top of the 34-story tower. According to the Newmark Knight Frank team that handles leasing for the building, the previously highest priced deal was in the $140s per s/f. That rate, already remarkable, is what the building's brokers are now asking for another block of empty space in the tower's mid-rise, on floors 21-24.

Some brokers said that the $160 per s/f rent--a rate that, if it were signed today, would be the highest price ever paid for an office lease in Manhattan--has encouraged tenants to examine the building's previously unquestioned cache.

Built in 1929, 745 Fifth Avenue, for one thing, is considerably older than many other top ranked properties. Its age, however, is what one of the building's brokers, Newmark Knight Frank's Scott Klau, said was one of its strengths.

"This is the kind of building for a tenant who wants to be in a property with an excellent location, tremendous views, and that sense of old world charm," Klau said.

Whether the building is able to achieve a rate at or near its asking price will determine if the market agrees with Klau. That there are questions surrounding a longstanding lynchpin of luxury like 745 Fifth Avenue to begin with, shows how even the most established entries in the trophy market can't avoid some bit of skepticism when pursuing record rates.

Overall, the prevailing opinion among brokers is that the building, if it doesn't capture $160 per s/f, would very likely command a rate very close to what it is seeking. It is common for brokers, even in high-end buildings, to bargain down slightly from a space's sticker price during the course of a leasing negotiation.

But if competing buildings have to slash asking rents by a significant margin or simply can't garner rental hikes commensurate with the market's gains, it could thrust prevailing perceptions of which spaces are the most desirable into upheaval. The results may impact the hierarchy of prestige among high-end buildings that landlords and brokers leverage to compete with one another. That subtle ranking can be important for top buildings because the price of space is often based off of the rents a competitor has achieved. If a building is considered to be of a higher caliber, that primacy will likely allow it to consistently reap higher rates than its peers.

Prestige is important to high end buildings not only because it solidifies a building's place among the competition, it also operates like a feedback mechanism.

If a building is able to sign tenants for jaw dropping rents, those deals act as vouchers for the value of its space and bring it cache just as much as its amenities and location do. In this way, deals that get done at exorbitant rates in a building tend to perpetuate more deals at similarly lofty, or even higher prices. The GM Building and 9 West 57th Street are examples of this.

Their reputation as not only luxury office properties but buildings where tenants routinely pay record rates is as important to the reputation of the two buildings as their park views and amenity-packed spaces. According to brokers, 9 West 57th Street is asking for the highest ever rate in the city, $200 per s/f for its top floor, a vacant 30,000 s/f space.