Well AMD just announced that they will be discontinuing all manufacturing and support for socket 754 so you should sell it while you can still get a decent price.
The Ultra-D and SLI board are almost the same Sevenor. The only thing that really seperates them is one resistor on the chipset which you can easily turn an Ultra-D into a SLI board by closing (connecting) the two spots of the resistor as seen here: