Picking up on both DrF's and MDM's comments ...
In my 457b -- which is so similar to yours that I thought we may work for the same employer -- I was 100% in a Vanguard target fund until they made the Vanguard Institutional Index (VIIIX, in my case) available.So, I went 100% in VIIIX. All the Vanguard target funds in my 457b have 0.10 expense ratio, but VIIIX is 0.02, so I made the switch.
VIIIX is similar to VTSAX. Take a look this ..
http://jlcollinsnh.com/2011/06/14/what-we-own-and-why-we-own-it/Then take a look at the 'stock series'. It brought a lot of MMM philosophy into focus for me.
http://jlcollinsnh.com/stock-series/BTW, I'm 44 and shooting to FIRE in ~5 years
Like MRM, I also see your pension as a bond fund. I get my bonds elsewhere in my portfolio right now, but I consider my pensions as bonds.