Wasn't thinking you had the X800XL. I'd say stay with that looking at just performance alone, but you bring up a good point with ebay. I was searching ebay for X800XL's a couple weeks ago, amazed to see just what they are selling for. You may get back almost what you spend on the HIS AR. Then the small speed boost and more advanced features become more interesting.
I'm running the X1650XT benchmarks throughout this week, but started them last night. I can tell you that a couple hours into it, it's been completetly stable on an old Antec 400W smartpower with just a single 20Amp 12v rail. I was going to upgrade the PSU, but it had been stable with an X800XTpe, so I figured I let it have a shot with the X1650XT. It's running one dvd/cdrw combo drive, 1 hdd, an NF2 and XP3200+ clocked athlon XP, 1GB ram, sound card, and 5-80mm case fans. I lent my X800XL to a friend so can't add it to the comparison it for you, but I did run benchies on an X800XTpe and an X1650 pro so far. I want to work through all games at reference XT speeds, then do them again at HIS Turbo speeds.
Anyway, only did farcry so far on the XT, in which the reference clocked X1650XT was dead even (within 1 fps) with the X800XTpe running 12x10 4xaa/8xaf. Of course, can't compare HDR as the X800XTpe can't do that, but the X1650XT destroyed the X1650 pro running HDR at 12x10, and even 10x7. I'm looking forward to doing Oblivion, NFS:carbon, Fear and HL2 Lost Coast on this thing; curious to see exactly how it will stack up to the X800XTpe.