Regular picture framing glass filters about 49% of the UV. As fdi has indicated that UV glass such as TruVue Conservation glass filters 97% of the UV and the Cyro Acrylite (Plexiglass) filters 98% of the UV. To avoid some of the issues of scratching the Acrylite that Scott has mentioned, Cyro makes the AR OP3 -abrasive resistant, optically pure (3) which is abrasively resistant. But it is very expensive; but it does scratch and it is a static magnet. I normally use glass up to 32" X 40" in size. You will have better luck using glass in wooden frames rather than metal because the wood will absorb, while the metal transmits shocks.
As to the size, weight and concerns for breakage, though I have used the Cyro AR OP3 for many pieces framed in wood as large as 40" x 48". I will say however, after framing one piece in that size (from original 40" X 60") in Museum Glass (TruVue's top of the line), my preference would be for the Museum Glass. Museum Glass by the way is an antireflective (not non glare), UV protective glass. The Museum Glass will get heavy in this size, and the frames need to be substantial enough to support the contents.
Museum Glass is extremely expensive, but it does everything that TruVue says. It reduces or eliminates most reflection, absorbs 97% of the UV, allows 96% of the visible light to pass through allowing the image to appear sharper, with brighter more vibrant color, and higher contrast.
As Scott has indicated though, there is concern about torsional forces, impact, etc. with glass when it gets large. The glass needs to be handled with some care.
Here is a cost comparison with Picture Framing Glass as the basis:
Picture Framing Glass: 1X
TruVue UV Conservation Clear Glass: 2-3X
Cyro AR OP3 Acrylite (in 4' X 8' sheets): 8X
TruVue Museum Glass: 17X
Rich