06 used RT vs 06 new RT

[cwm1515]

I have come to a crossroads. I'm trying to find the best deal and have come across this fork in the road. A dealer down the road from me has an 06 RT on their lot. The new 06s have a $4000.00 rebate right now. I figure since it's a 06 and the 08s will be in soon, I should be able to get it a little below invoice plus the rebate. I figure this would probably get me out the door somewhere in the $25,000.00 neighborhood. There is another dealer that has an 06 used w/ 21,000 miles for 21,995. I'm sure I could get them down to 20,500 and about 22,000 out the door. I may also be trading in my 04 F150 XLT. which is the better route to take. Can I bargain better on trade in if need be w/ the used car or new one. I've never traded a car in, I've always sold and then bought. Any advice would be appreciated.