There is a big difference between the two strategies - Investing in the Russel 3000 would be much more conservative than your current allocation.
The Russel 3000 is market cap weighted. This means that you get much more of the large cap stocks than your current allocation. The Russel 3000 currently (this will fluctuate depending on market forces) looks about like this:
Large-Cap - 72.44%
Mid-Cap - 19.13 %
Small-Cap - 8.43 %
Your current allocation of the S&P 500 fund and Russel 2000 money looks like:
Large-Cap - 56.25 % (.45 / .8)
Mid-Cap - 4.58 % (.1046 * .35 / .8)
Small-Cap - 39.17 % (.8955 * .35 / .8)
So if you switch to all Russel 3000, you'd be owning more Large Caps, more Mid Caps and less Small Caps. Basically it would shift you more towards larger companies - so (theoretically) less risk and less reward which is the definition of a more conservative allocation.