Larry, there's a little more difference than that. As Lorenzo indicated, the 3310 can be viewed as an upgraded 2809, while the 4310 is the upgraded 3808. The 3808 has slightly more power, although the 3310 should have more than enough for nearly all circumstances and the 3808 edge wouldn't be significant.
The 3310 has Audyssey MultEQ, which is one step down from MultEQ XT on the 3808, which has more measuring positions and higher resolution filters for more accurate results.
On the other hand, the 3310 has the Anchor Bay video processor, which is a significantly better upscaler/deinterlacer than the rather average Faroudja processor on the 3808.
The decision involves balancing features against price and isn't all that simple.
