No offense, but I wouldn't have posted if I didn't know, for a fact, what processors and mobos are applicable to the GX280. As a rule, when I don't know what I'm talking about, I keep my mouth shut.
First of all, I didn't use the Intel ID tool, I looked at the processors that are already working in my Dell GX280's and the corresponding motherboards - I've got about 30 of them ranging from 2.8ghz to 3.8ghz. Dell's M8995 is an SL82U (3.8ghz), Dell's D7464 is an SL7Q2 (3.6ghz). THERE IS NO QUESTION ABOUT THIS!!! Both work perfectly in the X6554 motherboard, but not in many of the earlier GX280 motherboards.
Second, entering the service tag on Dell's website is of no value whatsoever. If you want to upgrade your processor, it isn't going to be the same as the original one listed on the Dell build sheet and it's not going to tell you if an upgraded processor is going to work in the original motherboard. In many cases, the Dell processor is listed on the support website build sheet for your particular computer, but the Dell motherboard number is not.
Also, you really don't need to know or care the Dell number for the 2.8ghz processor originally installed by Dell if you are upgrading to a 3.8ghz processor. The Dell Support idea really sucks and will cost you hours and hours of chat (as it did me with 9 different Dell Techs) with very little in the way of satisfaction. They told me to replace the power supply (not necessary) and that the motherboards are interchangeable (not true). They couldn't tell me (or didn't want to tell me) the S-Spec (Intel) number of the processors that were installed in their computers. In fact, Dell said that they would sell me the Intel SL82U (Dell's M8995 3.8ghz) for - get this - $873 - well over twice the price of the complete GX280!!! I bought it for $32 - and it is working just fine in my Dell, with the X6554 motherboard that I bought for $15.99.
I indicated that I was working on this for a couple of months, sifting through procedures and parts that worked as well as the ones that didn't work. I didn't come back to this website with a solution that isn't valid. Dell tech support knew NOTHING about what processors (there are about 10 of them) work in what GX280 motherboards (there are about 16).
Bottom Line - Intel's SL82U and SL7Q2 WILL work perfectly in the GX280 if you have an X6554 motherboard.